FILLER COMPOSITIONS COMPRISING MICROFIBRILLATED CELLULOSE AND MICROPOROUS INORGANIC PARTICULATE MATERIAL COMPOSITES FOR PAPER AND PAPERBOARD APPLICATIONS WITH IMPROVED MECHANICAL PROPERTIES

Background

FIELD OF INVENTION

[0001] The present invention relates to methods of manufacturing paper comprising microfibrillated cellulose (“MFC”) and bulky microporous inorganic particulate material with improved mechanical properties through selection of bulky microporous inorganic particulate materials having optimal particle sizes and particle size distributions.

BACKGROUND OF THE INVENTION

[0002] Inorganic particulate material is commonly used in graphic papers to enhance optical and printing properties. Because inorganic particulate material (also referred to herein as “minerals and “filler”) is substantially less expensive than pulp fibres, use of inorganic particulate material also allows the papermaker to save costs. The amount of inorganic particulate material that can be used is limited because of the effect the inorganic particulate material has on the strength properties of paper, both in the wet state during manufacture and after drying.

[0003] During manufacture, the most important property which limits the inorganic particulate material content is the tensile strength of the wet paper after pressing. On most paper machines the paper is passed unsupported from the press to the dryer section and thus is held in tension whilst still at a relatively high-water content of up to 60%.

[0004] After drying, many paper grades require a minimum tensile, burst and tear strength, as well as tensile strength in the ‘Z’ direction (perpendicular to the plane of the paper) in order to resist damage during printing and converting processes. Other important sheet properties include resistance to bending and sheet bulk or thickness.

[0005] The addition of microfibrillated cellulose (MFC) has been established as a cost- effective way to increase many of the important strength properties of paper, including wet strength during manufacture, and thus enable higher inorganic particulate material content to be used and to save costs. However, the addition of MFC and the increase in inorganic particulate material content typically both have the effect of densifying the paper, leading to a reduction in sheet thickness.

[0006] Conventional filler compositions used in papermaking, such as ground calcium carbonate (GCC) and kaolin can give a slight increase in the thickness of paper per unit mass of fibre, since some inorganic particulate material particles occupy areas between overlapping fibres which would otherwise be tightly bonded together and increase the spacing between the fibres. However, the majority of particles are located in the void spaces in the fibre network that would otherwise be empty, and given their higher density compared with fibres the net effect of replacing fibre with filler is to densify the paper.

[0007] MFC bonds strongly to the fibres and draws them together, which also reduces paper bulk and thickness. Since the bending stiffness of a sheet of paper is very sensitive to its thickness, the use of MFC to increase inorganic particulate material content can also have a detrimental effect on this property. As a result, the increase in inorganic particulate material content achievable with the addition of MFC is often limited by the bulk and stiffness of the paper rather than its strength

Microporous inorganic particulate materials

[0008] Some types of filler, such as calcined clays and scalenohedral and aragonite precipitated calcium carbonates (PCC), consist of aggregates of particles with open porous structures (i.e. , these are examples of microporous inorganic particulate materials). Calcined clays are described in U.S. Patent No. 3,586,523, which is hereby incorporated herein by reference in its entirety. Such calcined kaolin clays are substantially anhydrous, amorphous aluminum silicates which are obtained by calcining a specific type of kaolin clay, for example, hard sedimentary kaolin clay.

[0009] Precipitated calcium carbonate (PCC) in clustered form is known in the art as disclosed in U.S. Patent No. 5,695,733, which is hereby incorporated by reference in its entirety. The PCC is produced in a unique clustered form having a substantial proportion of particles having a prismatic morphology. By controlling the solution environment utilized to produce PCC, i.e., the slaking of lime (calcium oxide), temperature of carbonation and the rate of introduction of carbon dioxide, either calcite, aragonite, or vaterite are produced.

Again, depending upon the process conditions calcite may have either prismatic, scalenohedral or rhombohedral crystal forms.

[0010] Other examples of microporous inorganic particulate materials include chemically aggregated filler materials. Examples of such chemically aggregated fillers may be found in U.S> Patent No. 4,072,537, which is hereby incorporated herein in its entirety. Such microporous inorganic particulate materials comprise a composite silicate material comprising a clay component and a metal silicate component. The clay component is typically kaolin clay or kaolinite and the metal silicate material is typically a water-soluble alkali metal silicate, for example sodium silicate.

[0011] As described in the ‘537 patent, preferred methods for preparing the composite pigment comprise the steps of, (a) forming an aqueous suspension of a clay pigment, (b) blending into the clay slurry a quantity of a salt such as calcium chloride, (c) metering into the slurry of clay and salt at high shear a quantity of a silicate component such as sodium silicate, and, optionally, (d) adjusting the pH of the slurry with the addition of alum to a pH no lower than pH 4, before (e) filtering and washing the precipitated product to remove any soluble salts. Such microporous composite silicate material is either used directly in a papermaking process or dried and used later. Additional microporous inorganic particulate material includes materials such as diatomaceous earth and expanded perlite.

[0012] All of foregoing materials microporous inorganic particulate materials consist of particles which contain rigid internal void spaces that persist through paper pressing and drying, and should also remain largely intact after calendering.

[0013] Scalenohedral PCC, calcined clays and chemically aggregated fillers achieve this structure by forming open aggregates of smaller particles and bonding the particles strongly where they contact each other. Diatomaceous earth consists of particles which naturally contain pores. Milled expanded perlite consists of fragments of micron-sized glass bubbles. Thus, microporous inorganic particulate materials comprise discrete particles or aggregates of particles with outer dimensions of several microns, which contain void spaces within the volume defined by the outer dimensions which are several times smaller than said outer dimensions. Collectively, the foregoing inorganic particulate material are designated herein as “microporous inorganic particulate materials” for the purpose of the present invention. [0014] When used in paper, these microporous inorganic particulate materials have a much larger effect, per unit mass of added particulate material, on the spacing of the fibres than solid filler particles. This makes them more detrimental to paper strength, but generates increased light scattering which is beneficial to optical properties.

[0015] Another effect of inorganic particulate materials is always to increase sheet porosity (air permeability), which is a significant disadvantage in printing and converting processes. The effective density of the microporous inorganic particulate materials is also lower than that of solid fillers, and the combination of these effects can lead to an increase in sheet bulk and thickness as fibre is substituted for filler. [0016] For scalenohedral PCC (an example of microporous inorganic particulate material), the effect of agglomeration on strength can be offset somewhat by controlling the particle size distribution to a narrow range (thus eliminating ultrafine particles which are very detrimental to paper strength) and using a larger median particle size than is optimum for light scattering. However, if the particle or agglomerate size is too large, then light scattering efficiency is lost.

Microflbrillated cellulose

[0017] Various methods of producing microflbrillated cellulose (“MFC”) are known in the art. Certain methods and compositions comprising microflbrillated cellulose are produced by grinding procedures are described in WO-A-2010/131016. Husband, J. C., Svending, P., Skuse, D. R., Motsi, T., Likitalo, M., Coles, A., FiberLean Technologies Ltd., 2015, “Paper filler composition,” PCT International Application No. WO-A-2010/131016, the contents of which is hereby incorporated by reference in its entirety. MFC produced by the described grinding processes may include the co-grinding of cellulose-containing fibres with inorganic particulate material. Alternatively, MFC may be produced by grinding cellulose fibres in the presence of grinding media other than inorganic particulate material. Paper products comprising such microflbrillated cellulose have been shown to exhibit excellent paper properties, such as paper burst and tensile strength. The methods described in WO-A- 2010/131016 also enable the production of microflbrillated cellulose economically.

[0018] W02010/131016 describes a grinding procedure for the production of microflbrillated cellulose with or without inorganic particulate material. Such a grinding procedure is described below. In an embodiment of the process set forth in WO-A-2010/131016, the process utilizes mechanical disintegration of cellulose fibres to produce microflbrillated cellulose (“MFC”) cost-effectively and at large scale, without requiring cellulose pre- treatment. An embodiment of the method uses stirred media detritor grinding technology, which disintegrates fibres into MFC by agitating grinding media beads. In this process, a mineral such as calcium carbonate or kaolin is added as a grinding aid, greatly reducing the energy required. Husband, J. C., S vending, P., Skuse, D. R., Motsi, T., Likitalo, M., Coles, A., FiberLean Technologies Ltd., 2015, “Paper filler composition,” U.S. Pat. US9127405B2, which is hereby incorporated herein by reference.

[0019] Notwithstanding the foregoing advances, there remains a need to optimize paper filler compositions comprising MFC and inorganic particulate material through judicious selection and control of inorganic particulate material particles sizes and particle size distributions to maintain sufficiently low porosity, high brightness and opacity and both wet and dry strength properties, including, minimum tensile, burst and tear strength, as well as tensile strength in the ‘Z’ direction (perpendicular to the plane of the paper) of paper and paperboard and to resist damage during printing and converting processes while optimizing resistance to bending and sheet bulk or thickness.

SUMMARY OF THE INVENTION

[0020] In accordance with the description, Figures, Examples and claims of the present specification, the inventors have discovered processes for the manufacture of paper and paperboard having improved mechanical properties through preparation and use of MFC and one or more microporous inorganic particulate material based on the particle size and particle size distribution of the one or more microporous inorganic particulate material.

[0021] The present invention is based on the use of microfibrillated cellulose and microporous inorganic particulate material, which are added to a papermaking furnish to produce paper and paperboard having enhanced mechanical properties that are not substantially degraded or are maintained or even improved when the compositions of MFC and microporous inorganic particulate material are utilized in lieu of MFC and conventional inorganic particulate material alone. The microfibrillated cellulose and microporous inorganic particulate material can be added to a papermaking furnish separately mish or as a filler composition comprising the MFC and the one or more microporous inorganic particulate material.

[0022] The present inventors have surprisingly found that the use of MFC in combination with one or more microporous inorganic particulate material, i.e., inorganic particulate material with a coarser (larger) than conventional particle and agglomerate size, can allow a substantial increase in the inorganic particulate material content of graphic papers whilst maintaining the required strength, bulk, stiffness and porosity properties. Losses in bulk and stiffness resulting from the use of MFC are offset by the high bulk contribution from the one or more microporous inorganic particulate material, and losses in strength from the use of a high content of microporous inorganic particulate material is offset by the use of the MFC. The MFC also offsets the typical increase in porosity associated with microporous inorganic particulate materials and the increased content of MFC and microporous inorganic particulate material offsets the loss of light scattering efficiency associated with using a microporous inorganic particulate material with a coarser than optimum particle size.

[0023] In accordance with the various aspects and embodiments of the present disclosure the one or more microporous inorganic particulate material comprises coarse particle size inorganic particulate material and agglomerates of coarse particle size microporous inorganic particulate material having a median particle size (d ₅₀ ) ranging from about 3 μm to about 50 μm, such as, for example, from about 5 μm to about 30 μm, from about 10 μm to about 30 μm, from about 15 μm to about 25 μm, from about 20 μm to about 30 μm, from about 3 μm to about 15 μm, from about 5 μm to about 15 μm, from about 5 μm to about 10 μm, from about 2 μm to about 6 μm, and, particularly preferred between 3 μm and 6 μm, as measured by sedimentation methods described herein and as known in the art.

[0024] Also in accordance with the various aspects and embodiments of the present disclosure, the term mechanical properties comprises one or more of Tensile Elongation, Tensile Stiffness, Bulk, and Bending Stiffness. The foregoing properties may be measured by methods described herein and as well known in the art of making paper and paperboard. [0025] In an aspect of the present disclosure, there is disclosed a paper or paperboard filler composition comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material for addition to a papermaking furnish for the manufacture of paper or paperboard, wherein the MFC and the one or more microporous inorganic particulate material impart mechanical properties to the paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing MFC and the one or more microporous inorganic particulate material. [0026] In another aspect of the present disclosure, there is disclosed a paper or paperboard filler composition comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material for use in a method for making a papermaking furnish for the manufacture of paper or paperboard, wherein the MFC and the one or more microporous inorganic particulate material impart mechanical properties to the paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing MFC and the one or more microporous inorganic particulate material [0027] In another aspect of the present disclosure, there is disclosed a paper or paperboard filler composition comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material for addition to a papermaking furnish for the manufacture of paper or paperboard, wherein the MFC is obtained by a co-grinding process using the same or different microporous inorganic particulate material and/or a conventional non-agglomerated inorganic particulate material and a fibrous substrate containing cellulose; and wherein the MFC and the one or more microporous inorganic particulate material impart mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing MFC and the one or more microporous inorganic particulate material.

[0028] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or is selected from the group consisting of) calcined clay, kaolin, kaolinite, amorphous aluminum silicates, Scalenohedral precipitated calcium chloride, aragonite precipitated calcium carbonate, chemically aggregated filler materials, diatomaceous earth, and milled expanded perlite.

[0029] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or consists essentially of or consists of) calcined clay.

[0030] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or consists essentially of or consists of) kaolin. [0031] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or consists essentially of or consists of) kaolinite.

[0032] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or consists essentially of or consists of) amorphous aluminum silicates.

[0033] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or consists essentially of or consists of) Scalenohedral precipitated calcium carbonate.

[0034] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or consists essentially of or consists of) aragonite precipitated calcium carbonate.

[0035] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or consists essentially of or consists of) chemically aggregated filler materials.

[0036] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or consists essentially of or consists of) diatomaceous earth.

[0037] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material comprises (or consists essentially of or consists of) milled expanded perlite.

[0038] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the MFC and the one or more microporous inorganic particulate material may be added separately or may be added together as a filler composition to the papermaking furnish. [0039] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the papermaking furnish comprises one or more pulp selected from softwood pulps.

[0040] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the softwood pulp is selected from (or selected from the group consisting of) spruce, pine, fir, larch and hemlock and mixed softwood pulps.

[0041] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the papermaking furnish comprises one or more pulp selected from (or selected from the group consisting of) hardwood pulps

[0042] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the hardwood pulp is selected from (or selected from the group consisting of) eucalyptus, aspen and birch, and mixed hardwood pulps.

[0043] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the pulp source for the papermaking furnish is selected from (or consists essentially of or consists of) eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp, cotton pulp, acacia and mixtures thereof

[0044] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the pulp source for the papermaking furnish is selected from (or consists essentially of or consists of) Nordic Pine, Black Spruce, Radiata Pine, Southern Pine, Enzyme-Treated Nordic Pine, Douglas Fir, Dissolving Pulp, Birch (including Birch #1, Birch #2 set forth herein), Eucalyptus, Acacia, Mixed European Hardwood, Mixed Thai Hardwood, Recycled Paper, Cotton, Abaca, Acacia, Sisal, Bagasse, Kenaf, Miscanthus, Sorghum, Giant

Reed and Flax. [0045] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is selected from one or more of Tensile Strength, Tensile Elongation, Bulk, Tensile Stiffness, Bending Stiffness, Porosity, Burst, Tear Strength, and Tensile Strength in the ‘Z’ direction.

[0046] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is Tensile Strength.

[0047] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is Tensile Elongation.

[0048] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is Bulk.

[0049] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is Tensile Stiffness.

[0050] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is Bending Stiffness.

[0051] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is Porosity.

[0052] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is Burst.

[0053] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is Tear Strength.

[0054] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the mechanical property is Tensile Strength in the ‘Z’ direction. [0055] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the microfibrillated cellulose has a modal fibre particle size ranging from about 0.1 μm-500 μm.

[0056] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, microfibrillated cellulose has a modal fibre particle size of at least about 0.5 μm, at least about 10 μm, at least about 50 μm, at least about 100 μm, at least about 150 μm, at least about 200 μm, at least about 300 μm, or at least about 400 μm.

[0057] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material has a median particle size (d ₅₀ ) ranging from about 3 μm to about 50 μm, from about 5 μm to about 30 μm, from about 10 μm to about 30 μm, from about 15 μm to about 25 μm, from about 20 μm to about 30 μm, from about 3 μm to about 15 μm, from about 5 μm to about 15 μm, from about 5 μm to about 10 μm, from about 3 μm to about 6 μm, or from about 3 to about 5 μm, as measured by laser light scattering.

[0058] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material and microfibrillated cellulose composite may be associated with one or more dispersing agents such as those selected from the group comprising (or elected from the group consisting of) homopolymers or copolymers of poly carboxylic acids and/or their salts or derivatives, esters based on, acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid; acryl amide or acrylic esters, methylmethacrylate, or mixtures thereof; alkali polyphosphates, phosphonic-, citric- and tartaric acids and the salts or esters thereof; and mixtures thereof. [0059] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material and microfibrillated cellulose composite is provided in the form of a powder.

[0060] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material and microfibrillated cellulose composite is provided in the form of a suspension, or an aqueous suspension and in alternative embodiments the aqueous suspension is a pumpable liquid.

[0061] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, wherein the one or more microporous inorganic particulate material comprises a blend of a first and second microporous inorganic particulate material, wherein the ratio of the first microporous inorganic particulate material to the second microporous inorganic particulate material may range from about 10:90 to about 90:10 by weight, or from about 20:80 to about 80:20 by weight, or from about 25:75 to about 75:25 by weight, or from about 40:60 to about 60:40 by weight, or from about 50:50 by weight.

[0062] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the binder composition further comprises a binder and in an embodiment may be an inorganic or organic binder. In other embodiments, the binder may be an alkali metal silicate, such as sodium silicate or potassium silicate.

[0063] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the binder composition has a weight ratio of microfibrillated cellulose to the one or more microporous inorganic particulate material on a dry weight basis is from 1 :5 to 5: 1, or from 1:3 to 3: 1, or from 1:2 to 2:1, or from 1:1.5 to 1.5 to 1, or from 1:1.

[0064] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the total content of the one or more microporous inorganic particulate material is present in an amount of from 10 wt. % to 95 wt.% on a dry weight basis of the filler composition, or from 15 wt.% to 90 wt.%, or from 20 to 75 wt.%, or from 25 wt.% to 67 wt.%, or from 33 to 50 wt.% on a dry weight basis of the filler composition.

[0065] In another aspect of the present disclosure there is disclosed a method of making a papermaking furnish comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material, the method comprising the steps of: adding the one or more microporous inorganic particulate material to the papermaking furnish; adding the MFC to the papermaking furnish; wherein the MFC and the one or more microporous inorganic particulate material impart mechanical properties to the paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing the microfibrillated cellulose and the one or more microporous inorganic particulate material.

[0066] In another aspect of the present disclosure there is disclosed a method of making a papermaking furnish comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material, the method comprising the steps of: adding the one or more microporous inorganic particulate material to the papermaking furnish; adding the MFC to the papermaking furnish; wherein the MFC is obtained by a co-grinding process using the same or different microporous inorganic particulate material and/or a conventional non-agglomerated inorganic particulate material and a fibrous substrate comprising cellulose; and wherein the MFC and the one or more microporous inorganic particulate material impart mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing the microfibrillated cellulose and the one or more microporous inorganic particulate material.

[0067] In another aspect of the present disclosure there is disclosed a method of making a papermaking furnish comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material, the method comprising the steps of: adding a filler composition comprising MFC and the one or more microporous inorganic particulate material to the papermaking furnish; wherein the MFC and the one or more microporous inorganic particulate material impart mechanical properties to the paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing the microfibrillated cellulose and the one or more microporous inorganic particulate material.

[0068] In another aspect of the present disclosure there is disclosed a papermaking furnish comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material, the method comprising the steps of: adding a filler composition comprising MFC and the one or more microporous inorganic particulate material to the papermaking furnish; wherein the MFC is obtained by a co- grinding process using the same or different microporous inorganic particulate material and/or a conventional non-agglomerated inorganic particulate material and a fibrous substrate comprising cellulose; and wherein the MFC and the one or more microporous inorganic particulate material impart mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing the microfibrillated cellulose and the one or more microporous inorganic particulate material. [0069] In another aspect of the present disclosure there is disclosed a paper or paperboard made from a papermaking furnish comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material, the method comprising the steps of: adding a filler composition comprising MFC and the one or more microporous inorganic particulate material to the papermaking furnish; wherein the filler composition imparts mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing the MFC and the one or more microporous inorganic particulate material.

[0070] A method of making a paper or paperboard with improved mechanical properties, the method comprising the steps of: preparing a papermaking furnish for production of paper or paperboard; adding one or more microporous inorganic particulate material to the papermaking furnish; adding microfibrillated cellulose (MFC) to the papermaking furnish; wherein the MFC and the one or more microporous inorganic particulate material are added separately to the papermaking furnish or as a filler composition comprising the MFC and the one or more microporous inorganic particulate material; manufacturing the paper or paperboard from the papermaking furnish by dewatering and drying the papermaking furnish; wherein the MFC and the one or more microporous inorganic particulate materials impart mechanical properties to the paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing MFC and microporous inorganic particulate material.

[0071] In another aspect of the present disclosure, there is a method of making method of making a paper or paperboard from a papermaking furnish comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate materials, the method comprising the steps of: adding a filler composition comprising MFC and the one or more microporous inorganic particulate material to the papermaking furnish; wherein the MFC is obtained by a co- grinding process using the same or different microporous inorganic particulate material and/or a conventional non-agglomerated inorganic particulate material and a fibrous substrate comprising cellulose; and wherein the filler composition imparts mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing the MFC and one or microporous inorganic particulate material. In an embodiment, the MFC and the one or more microporous inorganic particulate material are added separately to the papermaking furnish or as a filler composition comprising the MFC and the one or more microporous inorganic particulate material.

[0072] In another aspect of the present disclosure, there is method of making a paper or paperboard from a papermaking furnish comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate materials, the method comprising the steps of: adding the one or more microporous inorganic particulate material to the papermaking furnish; adding MFC to the papermaking furnish; wherein the MFC and the one or more microporous inorganic particulate material imparts mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing the microfibrillated cellulose and the one or more microporous inorganic particulate material. In an embodiment, the MFC and the one or more microporous inorganic particulate material are added separately to the papermaking furnish or as a filler composition comprising the MFC and the one or more microporous inorganic particulate material. [0073] In another aspect of the present disclosure, there is a method of making a paper or paperboard from a papermaking furnish comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate materials, the method comprising the steps of: adding the one or more microporous inorganic particulate material to the papermaking furnish; adding the MFC to the papermaking furnish; wherein the MFC is obtained by a co-grinding process using the same or different microporous inorganic particulate material and/or a conventional non-agglomerated inorganic particulate material and a fibrous substrate comprising cellulose; and wherein the MFC and the one or more microporous inorganic particulate material imparts mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing the MFC and the one or microporous inorganic particulate material. In an embodiment, the MFC and the one or more microporous inorganic particulate material are added separately to the papermaking furnish or as a filler composition comprising the MFC and the one or more microporous inorganic particulate material.

[0074] In another aspect of the present disclosure, there is a method of making a paper or paperboard with improved mechanical properties, the method comprising the steps of: preparing a papermaking furnish for production of paper or paperboard; preparing a filler composition comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material; adding the filler composition to the papermaking furnish; manufacturing a paper or paperboard from the papermaking furnish by dewatering and drying the papermaking furnish; wherein the filler composition imparts mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing MFC and microporous inorganic particulate material. In an embodiment, the MFC and the one or more microporous inorganic particulate material are added separately to the papermaking furnish or as a filler composition comprising the MFC and the one or more microporous inorganic particulate material.

[0075] In another aspect of the present disclosure, there is a method of making a paper or paperboard with improved mechanical properties, the method comprising the steps of: preparing a papermaking furnish for production of paper or paperboard; preparing a filler composition comprising microfibrillated cellulose (MFC) and one or more microporous inorganic particulate material; adding the filler composition to the papermaking furnish; manufacturing a paper or paperboard from the papermaking furnish by dewatering and drying the papermaking furnish; wherein the MFC is obtained by a co-grinding process using the same or different microporous inorganic particulate material and/or a conventional non- agglomerated inorganic particulate material and a fibrous substrate comprising cellulose; and wherein the filler composition imparts mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not MFC and the one or more microporous inorganic particulate material. In an embodiment, the MFC and the one or more microporous inorganic particulate material are added separately to the papermaking furnish or as a filler composition comprising the MFC and the one or more microporous inorganic particulate material.

[0076] In another aspect of the present disclosure, there is a method of making a paper or paperboard with improved mechanical properties, the improvement comprising: preparing a papermaking furnish for production of paper or paperboard; adding one or more microporous inorganic particulate material to the papermaking furnish; adding microfibrillated cellulose

(MFC) to the papermaking furnish; manufacturing a paper or paperboard from the papermaking furnish by dewatering and drying the papermaking furnish; wherein the MFC and the one or more microporous inorganic particulate materials impart mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing MFC and microporous inorganic particulate material. In an embodiment, the MFC and the one or more microporous inorganic particulate material are added separately to the papermaking furnish or as a filler composition comprising the MFC and the one or more microporous inorganic particulate material.

[0077] In another aspect of the present disclosure, there is a method of making a paper or paperboard with improved mechanical properties, the improvement comprising: preparing a papermaking furnish for production of paper or paperboard; adding one or more microporous inorganic particulate material to the papermaking furnish; adding microfibrillated cellulose (MFC) to the papermaking furnish; manufacturing a paper or paperboard from the papermaking furnish by dewatering and drying the papermaking furnish; wherein the MFC is obtained by a co-grinding process using the same or different microporous inorganic particulate materials and/or a conventional non-agglomerated inorganic particulate material and a fibrous substrate comprising cellulose; and wherein the MFC and the one or more microporous inorganic particulate materials impart mechanical properties to said paper or paperboard that are improved compared to paper and paperboard products made from an identical papermaking furnish not containing MFC and the one or more microporous inorganic particulate material. In an embodiment, the MFC and the one or more microporous inorganic particulate material are added separately to the papermaking furnish or as a filler composition comprising the MFC and the one or more microporous inorganic particulate material. [0078] In additional embodiments of the foregoing aspects and embodiments of the present disclosure, the one or more microporous inorganic particulate material is selected from the group comprising (or selected from the group consisting of) calcined clay, kaolin, kaolinite, amorphous aluminum silicates, Scalenohedral precipitated calcium chloride, aragonite precipitated calcium carbonate, chemically aggregated filler materials, diatomaceous earth, or milled expanded perlite.

[0079] In an embodiment, the one or more microporous inorganic particulate material comprises or is calcined clay.

[0080] In an embodiment, the one or more microporous inorganic particulate material comprises or is kaolin.

[0081] In an embodiment, the one or more microporous inorganic particulate material comprises or is kaolinite.

[0082] In an embodiment, the one or more microporous inorganic particulate material comprises or is amorphous aluminum silicate.

[0083] In an embodiment, the one or more microporous inorganic particulate material comprises or is Scalenohedral precipitated calcium carbonate.

[0084] In an embodiment, the one or more microporous inorganic particulate material comprises or is aragonite precipitated calcium carbonate.

[0085] In an embodiment, the one or more microporous inorganic particulate material comprises or is chemically aggregated filler materials.

[0086] In an embodiment, the one or more microporous inorganic particulate material comprises or is diatomaceous earth.

[0087] In an embodiment, the one or more microporous inorganic particulate material comprises or is milled expanded perlite. [0088] In an embodiment of the aspects of the present disclosure the papermaking furnish comprises one or more pulp selected from softwood pulps.

[0089] In an embodiment of the aspects of the present disclosure the softwood pulp is selected from (or is selected from the group consisting of) spruce, pine, fir, larch and hemlock or mixed softwood pulps.

[0090] In an embodiment of the aspects of the present disclosure the papermaking furnish comprises one or more pulp selected from hardwood pulp.

[0091] In an embodiment of the aspects of the present disclosure the hardwood pulp is selected from (or is selected from the group consisting of) eucalyptus, aspen and birch, or mixed hardwood pulps.

[0092] In an embodiment of the aspects of the present disclosure the pulp source for the papermaking furnish is selected from (or is selected from the group consisting of) eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp, acacia, cotton pulp, and mixtures thereof.

[0093] In an embodiment of the aspects of the present disclosure the pulp source for the papermaking furnish is selected from (or is selected from the group consisting of) Nordic Pine, Black Spruce, Radiata Pine, Southern Pine, Enzyme-Treated Nordic Pine, Douglas Fir, Dissolving Pulp, (Birch (including Birch #1, Birch #2 set forth herein), Eucalyptus, Acacia, Mixed European Hardwood, Mixed Thai Hardwood, Recycled Paper, Cotton, Abaca, Sisal, Bagasse, Kenaf, Miscanthus, Sorghum, Giant Reed and Flax.

[0094] In an embodiment of the aspects of the present disclosure the microfibrillated cellulose is prepared by a co-grinding process with one or more non-agglomerated inorganic particulate material utilized in preparation of the microfibrillated cellulose and one or more microporous inorganic particulate material composite. [0095] In an embodiment of the aspects of the present disclosure the microfibrillated cellulose has a fibre steepness of about 20 to about 50.

[0096] In an embodiment of the aspects of the present disclosure the microfibrillated cellulose has a d ₅₀ ranging from about 5 to about 500 μm, as measured by laser light scattering.

[0097] In an embodiment of the aspects of the present disclosure the microfibrillated cellulose has a d ₅₀ of equal to or less than about 400 μm, as measured by laser light scattering.

[0098] In an embodiment of the aspects of the present disclosure the microfibrillated cellulose has a d ₅₀ of equal to or less than about 200 μm, as measured by laser light scattering.

[0099] In an embodiment of the aspects of the present disclosure the microfibrillated cellulose has a d ₅₀ of equal to or less than about 200 μm, as measured by laser light scattering.

[00100] In an embodiment of the aspects of the present disclosure the microfibrillated cellulose has a d ₅₀ of equal to or less than about 150 μm, as measured by laser light scattering.

[00101] and

[00102] In an embodiment of the aspects of the present disclosure, the one or more microporous inorganic particulate material and microfibrillated cellulose composite is provided in the form of a powder.

[00103] In an embodiment of the aspects of the present disclosure, the one or more microporous inorganic particulate material and microfibrillated cellulose composite is provided in the form of a suspension. In another embodiment, the suspension may be an aqueous suspension. In a further embodiment, the aqueous suspension is a pumpable liquid. [00104] In an embodiment of the aspects of the present disclosure, the one or more microporous inorganic particulate material comprises a blend of a first and second microporous inorganic particulate material, wherein the ratio of the first microporous inorganic particulate material to the second microporous inorganic particulate material may range from about 10:90 to about 90:10 by weight, from about 20:80 to about 80:20 by weight, or from about 25:75 to about 75:25 by weight, or from about 40:60 to about 60:40 by weight, or from about 50:50 by weight.

[00105] In an embodiment of the aspects of the present disclosure, the method further comprises a binder. In another embodiment, the binder is an organic or inorganic binder. In a further embodiment, the binder is an alkali metal silicate, such as sodium silicate or potassium silicate.

[00106] In further embodiments of the aspects of the present disclosure, the weight ratio of microfibrillated cellulose to the one or more microporous inorganic particulate material on a dry weight basis is from 1:5 to 5:1, or 1:3 to 3:1, or 1:2 to 2:1, or 1:1.5 to 1.5 to 1, or about 1: 1.

[00107] In further embodiments of the aspects of the present disclosure, the total content of the one or more microporous inorganic particulate material is present in an amount of from 10 wt-% to 95 wt-% on a dry weight basis of the filler composition, from 15 wt.% to 90 wt.%, or from 20 to 75 wt.%, or from 25 wt.% to 67 wt.%, or from 33 to 50 wt-% on a dry weight basis of the filler composition.

[00108] Unless otherwise stated, particle size properties referred to herein for the inorganic particulate materials are as measured in a well-known manner by sedimentation of the particulate material in a fully dispersed condition in an aqueous medium using a Sedigraph 5100 machine as supplied by Micromeritics Instruments Corporation, Norcross, Ga., USA (telephone: +1 770 662 3620; web-site: www. micromeritics. com), referred to herein as a "Micromeritics Sedigraph 5100 unit". Such a machine provides measurements and a plot of the cumulative percentage by weight of particles having a size, referred to in the art as the 'equivalent spherical diameter' (e.s.d), less than given e.s.d values. The mean particle size d ₅₀ is the value determined in this way of the particle e.s.d at which there are 50% by weight of the particles which have an equivalent spherical diameter less than that d ₅₀ value.

[00109] In an embodiment of the aspects of the present disclosure the blend of the first and second inorganic particulate materials and the binder solution may be mixed with sufficient agitation to at least substantially uniformly distribute the binder composition (slurry or suspension) among the agglomeration points of contact of the blend of first and second inorganic particulate materials without damaging the structure of the first or second inorganic particulate materials.

[00110] In an embodiment of the aspects of the present disclosure the contacting is performed in a low-shear mixing apparatus.

[00111] In an embodiment of the aspects of the present disclosure the mixing may occur at about room temperature (i.e., from about 20° C. to about 23° C ).

[00112] In an embodiment of the aspects of the present disclosure the mixing may occur at about room temperature (i.e., from about 20° C. to about 50° C.)

[00113] In an embodiment of the aspects of the present disclosure the mixing may occur at about room temperature (i.e., from about 30° C. to about 45° C.)

[00114] In an embodiment of the aspects of the present disclosure the mixing may occur at about room temperature (i.e., from about 35° C. to about 45° C.) [00115] In an embodiment of the aspects of the present disclosure the contacting may include spraying the blend of first and/or first and second inorganic particulate materials with a binder composition (slurry or suspension).

[00116] In an embodiment of the aspects of the present disclosure the contacting is intermittent.

[00117] In an embodiment of the aspects of the present disclosure the contacting is continuous.

[00118] In an embodiment of the aspects of the present disclosure the binder may be present in a binder composition (slurry or suspension) in an amount less than about 40% by weight, relative to the weight of the binder solution. In some embodiments, the binder may range from about 1% to about 10% by weight.

[00119] The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described herein, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that any conception and specific embodiment disclosed herein may be readily utilized as a basis for modifying or designing other means for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent means do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that any description, figure, example, etc. is provided for the purpose of illustration and description only and is by no means intended to define the limits the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[00120] For a more complete understanding of the principles disclosed herein, and the advantages thereof, reference is made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[00121] Fig. 1 is a plot of Scott Bond, Bending Stiffness, Tensile Index, Bulk and Light Scattering properties for compositions comprising ground calcium carbonate (GCC) compositions at 20% and 30% levels with and without MFC compared to precipitated calcium carbonate (PCC) compositions at 20% and 30% levels with and without MFC.

[00122] Fig. 2 is a graph of Bending Stiffness in mN.m versus percentage filler proportion comprising PCC (remainder is GCC).

[00123] Fig. 3 is a graph of Light Scattering Coefficient (F10) in cm ² g ^-1 versus percentage filler proportion comprising PCC (remainder is GCC).

[00124] Fig. 4 is a graph of Tensile Index in N.m/g versus percentage filler proportion comprising PCC (remainder is GCC).

[00125] Fig. 5 is a graph of Scott Bond in J/m ² versus percentage filler proportion comprising PCC (remainder is GCC).

[00126] Fig. 6 is a graph of Tensile Index in N.m/g versus Sheet Filler Content in percentage PCC content.

[00127] Fig. 7 is a graph of Light Scattering (F10 S) versus Sheet Filler Content in percentage PCC content.

[00128] Fig. 8 is a graph of Bending Stiffness in mN versus Sheet Filler Content in percentage PCC content.

DETAILED DESCRIPTION OF THE INVENTION [00129] The titles, headings and subheadings provided herein should not be interpreted as limiting the various aspects of the disclosure. Accordingly, the terms defined below are more fully defined by reference to the specification in its entirety. All references cited herein are incorporated by reference in their entirety.

[00130] The present invention relates to filler composition comprising MFC and one or more microporous inorganic particulate material composite to be utilized in papermaking furnishes for the production of paper and paperboard with improved mechanical properties compared to paper and paperboard produced without MFC and one or more microporous inorganic particulate material.

Definitions and Headings

[00131] The titles, headings and subheadings provided herein should not be interpreted as limiting the various aspects of the disclosure. Accordingly, the terms defined below are more fully defined by reference to the specification in its entirety. All references cited herein are incorporated by reference in their entirety.

[00132] Unless otherwise defined, scientific and technical terms used herein shall have the meanings that are commonly understood by those of ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[00133] In this application, the use of “or” means “and/or” unless stated otherwise. In the context of a multiple dependent claim, the use of “or” refers back to more than one preceding independent or dependent claim in the alternative only.

[00134] The use of the word "a" or "an" when used in conjunction with the term "comprising" may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one." The use of the term "or" is used to mean "and/or' unless explicitly indicated to refer to alternatives only if the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and/or." Throughout this application, the term "about" is used to indicate that a value includes the inherent variation of error for the quantifying device, the method being employed to determine the value, or the variation that exists among the study subjects. For example, but not by way of limitation, when the term "about" is utilized, the designated value may vary by plus or minus twelve percent, or eleven percent, or ten percent, or nine percent, or eight percent, or seven percent, or six percent, or five percent, or four percent, or three percent, or two percent, or one percent. The use of the term "at least one" will be understood to include one as well as any quantity more than one, including but not limited to, 1, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, etc. The term "at least one" may extend up to 100 or 1000 or more depending on the term to which it is attached. In addition, the quantities of 100/1000 are not to be considered limiting as lower or higher limits may also produce satisfactory results. In addition, the use of the term "at least one of X, Y, and Z" will be understood to include X alone, Y alone, and Z alone, as well as any combination of X, Y, and Z.

[00135] The use of ordinal number terminology (i.e., "first", "second", "third", "fourth", etc.) is solely for the purpose of differentiating between two or more items and, unless otherwise stated, is not meant to imply any sequence or order or importance to one item over another or any order of addition.

[00136] As used herein, the term one or more microporous inorganic particulate material comprises coarse particle size inorganic particulate material and agglomerates of coarse particle size inorganic particulate material having a median particle size (d ₅₀ ) ranging from about 3 μm to about 50 μm, such as, for example, from about 5 μm to about 30 μm, from about 10 μm to about 30 μm, from about 15 μm to about 25 μm, from about 20 μm to about 30 μm, from about 3 μm to about 15 μm, from about 5 μm to about 15 μm, from about 5 μm to about 10 μm, from about 2 μm to about 6 μm, and, particularly preferred between 3 μm and 6 μm, as measured by sedimentation methods described herein and as known in the art.

[00137] As used herein, the terms "comprising" (and any form of comprising, such as "comprise", "comprises", and "comprised"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include"), or "containing" (and any form of containing, such as "contains" and "contain"), are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. Additionally, a term that is used in conjunction with the term "comprising" is also understood to be able to be used in conjunction with the term "consisting of or "consisting essentially of.” Similarly, the phrase “selected from” and words of like import may also include the phrase “selected from the group consisting of.”

[00138] As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

[00139] The fibrous substrate comprising cellulose (variously referred to herein as “fibrous substrate comprising cellulose,” “cellulose fibres,” “fibrous cellulose feedstock,” “cellulose feedstock” and “cellulose-containing fibres (or fibrous,” etc.) may be derived from virgin or recycled pulp or a papermill broke and/or industrial waste, or a paper streams rich in mineral fillers and cellulosic materials from a papermill.

[00140] As used herein, mechanical properties comprise one or more of the following properties: Tensile Strength, Tensile Elongation, Bulk, Tensile Stiffness, Bending Stiffness,

Porosity, Tensile, Burst, Tear Strength, and Tensile Strength in the ‘Z’ direction. [00141] As used herein, the term "substantially" means that the subsequently described event or circumstance completely occurs or that the subsequently described event or circumstance occurs to a great extent or degree. For example, when associated with a particular event or circumstance, the term "substantially" means that the subsequently described event or circumstance occurs at least 80% of the time, or at least 85% of the time, or at least 90% of the time, or at least 95% of the time. Conversely, when used to signify that the mechanical properties, such as tensile strength and/or bending stiffness are “not substantially degraded” or similar language, the degradation of tensile strength and/or bending stiffness are not diminished by more than 15%, or more than 10% or more than 5% from the properties of the control.

[00142] As used herein, the phrase "integer from X to Y" means any integer that includes the endpoints. For example, the phrase "integer from 1 to 5" means 1, 2, 3, 4, or 5.

Microflbrillated Cellulose

[00143] Microflbrillated cellulose (MFC), although well-known and described in the art, for purposes of the presently disclosed and/or claimed inventive concept(s), microflbrillated cellulose is defined as cellulose consisting of microfibrils in the form of either isolated cellulose microfibrils and/or microfibril bundles of cellulose, both of which are derived from a cellulose raw material. Thus, microflbrillated cellulose is to be understood to comprise partly or totally fibrillated cellulose or lignocellulose fibers, which may be achieved by a variety of processes known in the art.

[00144] As used herein, "microflbrillated cellulose" can be used interchangeably with "microfibrillar cellulose," "nanofibrillated cellulose," "nanofibril cellulose," "nanofibers of cellulose," "nanoscale fibrillated cellulose," "microfibrils of cellulose," and/or simply as

MFC." Additionally, as used herein, the terms listed above that are interchangeable with "microfibrillated cellulose" may refer to cellulose that has been completely microfibrillated or cellulose that has been substantially microfibrillated but still contains an amount of non- microfibrillated cellulose at levels that do not interfere with the benefits of the microfibrillated cellulose as described and/or claimed herein

[00145] By "microfibrillating" is meant a process in which microfibrils of cellulose are liberated or partially liberated as individual species or as small aggregates as compared to the fibres of the pre-microfibrillated pulp. Typical cellulose fibres (i. e. , pre-microfibrillated pulp) suitable for use in papermaking include larger aggregates of hundreds or thousands of individual cellulose fibrils

[00146] Microfibrillated cellulose comprises cellulose, which is a naturally occurring polymer comprising repeated glucose units. The term "microfibrillated cellulose", also denoted MFC, as used in this specification, includes microfibrillated/microfibrillar cellulose and nano-fibrillated/nanofibrillar cellulose (NFC), which materials are also called nanocellulose.

[00147] Microfibrillated cellulose is prepared by stripping away the outer layers of cellulose fibers that may have been exposed through mechanical shearing, with or without prior enzymatic or chemical treatment. There are numerous methods of preparing microfibrillated cellulose that are known in the art.

[00148] In a non-limiting example, the term microfibrillated cellulose is used to describe fibrillated cellulose comprising nanoscale cellulose particle fibers or fibrils frequently having at least one dimension less than 100 nm. When liberated from cellulose fibres, fibrils typically have a diameter less than 100 nm. The actual diameter of cellulose fibrils depends on the source and the manufacturing methods. [00149] The particle size distribution and/or aspect ratio (length/width) of the cellulose microfibrils attached to the fibrillated cellulose fiber or as a liberated microfibril depends on the source and the manufacturing methods employed in the microfibrillation process.

[00150] In a non-limiting example, the aspect ratio of microfibrils is typically high and the length of individual microfibrils may be more than one micrometer and the diameter may be within a range of about 5 to 60 nm with a number-average diameter typically less than 20 nm. The diameter of microfibril bundles may be larger than 1 micron, however, it is usually less than one

[00151] In a non-limiting example, the smallest fibril is conventionally referred to as an elementary fibril, which generally has a diameter of approximately 2-4 nm. It is also common for elementary fibrils to aggregate, which may also be considered as microfibrils.

[00152] In a non-limiting example, the microfibrillated cellulose may at least partially comprise nanocellulose. The nanocellulose may comprise mainly nano-sized fibrils having a diameter that is less than 100 nm and a length that may be in the micron-range or lower. The smallest microfibrils are similar to the so-called elemental fibrils, the diameter of which is typically 2 to 4 nm. Of course, the dimensions and structures of microfibrils and microfibril bundles depend on the raw materials used in addition to the methods of producing the microfibrillated cellulose. Nonetheless, it is expected that a person of ordinary skill in the art would understand the meaning of "microfibrillated cellulose" in the context of the presently disclosed and/or claimed inventive concept(s)

[00153] Depending on the source of the cellulose fibers and the manufacturing process employed to microfibrillate the cellulose fibres, the length of the fibrils can vary, frequently from about 1 to greater than 10 micrometers. [00154] A coarse MFC grade might contain a substantial fraction of fibrillated fibers, i.e. protruding fibrils from the tracheid (cellulose fiber), and with a certain amount of fibrils liberated from the tracheid (cellulose fiber).

[00155] In an embodiment, the microfibrillated cellulose may also be prepared from recycled pulp or a papermill broke and/or industrial waste, or a paper streams rich in mineral fillers and cellulosic materials from a papermill.

[00156] The fibrous substrate comprising cellulose may be added to a grinding vessel fibrous substrate comprising cellulose in a dry state. For example, a dry paper broke may be added directly to the grinder vessel. The aqueous environment in the grinder vessel will then facilitate the formation of a pulp.

Co-Grinding Process of Microfibrillated Cellulose and Inorganic particulate Material [00157] In an embodiment, the present invention is related to modifications, for example, improvements, to the methods and compositions described in WO-A-2010/131016, the entire contents of which are hereby incorporated by reference.

[00158] WO-A-2010/131016 discloses a process for preparing microfibrillated cellulose comprising microfibrillating, e.g., by grinding, a fibrous material comprising cellulose, optionally in the presence of grinding medium and inorganic particulate material. When used as a filler in paper, for example, as a replacement or partial replacement for a conventional mineral filler, the microfibrillated cellulose obtained by said process, optionally in combination with inorganic particulate material, was unexpectedly found to improve the burst strength properties of the paper. That is, relative to a paper filled with exclusively mineral filler, paper filled with the microfibrillated cellulose was found to have improved burst strength. In other words, the microfibrillated cellulose filler was found to have paper burst strength enhancing attributes. In one particularly advantageous embodiment of that invention, the fibrous material comprising cellulose was ground in the presence of a grinding medium, optionally in combination with inorganic particulate material, to obtain microfibrillated cellulose having a fibre steepness of from 20 to about 50.

Co-Processing of a Fibrous Substrate Comprising Cellulose and at least one Inorganic Particulate Material

[00159] As used herein, the terms “co-grinding (or “co-ground”) composite of microfibrillated cellulose and inorganic particulate material” refers to a composite obtained by a “co-grinding microfibrillation process,” wherein a fibrous substrate comprising cellulose is microfibrillated in an aqueous environment in a grinding apparatus in the presence of the at least one inorganic particulate material, and optionally a grinding medium other than the at least one inorganic particulate material (or stated differently by “co-processing” a fibrous substrate comprising cellulose in the presence of the at least one inorganic particulate material in a wet grinding apparatus and optionally in the presence of a grinding medium other than the at least one inorganic particulate material, which is removed after grinding, to produce microfibrillated cellulose). See the description below of an exemplary microfibrillation process and wet-grinding process.

[00160] After co-processing to form a co-processed microfibrillated cellulose and inorganic particulate material composite, additional inorganic particulate material may be added (e.g., by blending or mixing) to reduce the microfibrillated cellulose content of the co-processed microfibrillated cellulose and inorganic particulate material composite.

[00161] In an embodiment, the MFC may be manufactured using a tower mill or a screened grinding mill such as a stirred media detritor.

[00162] A stirred media mill consists of a rotating impeller that transfers kinetic energy to small grinding media beads, which grind down the charge via a combination of shear, compressive, and impact forces. A variety of grinding apparatus may be used to produce MFC by the disclosed methods herein, including, for example, a tower mill, a screened grinding mill, or a stirred media detritor.

The Microflbrillating Process

[00163] In accordance with a further aspect and embodiments of the present disclosure, there is provided a method of microflbrillating a fibrous substrate comprising cellulose in the presence of at least one inorganic particulate material. According to particular embodiments of the present methods, the microflbrillating step is conducted in the presence of an inorganic particulate material which acts as a microflbrillating agent. In accordance with another embodiment the microflbrillating step is conducted in the presence of an inorganic particulate material and a grinding medium other than the at least one inorganic particulate material, which is removed after grinding.

[00164] The microfibrillated cellulose utilized in the present invention is, however, not limited to a single manufacturing method. Such microfibrillation processes are presented for illustrative purposes.

[00165] By “microflbrillating” is meant a process in which microfibrils of cellulose are liberated or partially liberated as individual species or as smaller aggregates as compared to the fibres of the pre-microfibrillated cellulose-containing pulp. Typical cellulose fibres (i.e., pre-microfibrillated cellulose-containing pulp) suitable for use in papermaking include larger aggregates of hundreds or thousands of individual cellulose microfibrils. By microflbrillating the cellulose, particular characteristics and properties, including but not limited to the characteristic and properties described herein, are imparted to the microfibrillated cellulose and the compositions including microfibrillated cellulose and at least one inorganic particulate material. [00166] The step of microfibrillating may be carried out in any suitable apparatus. In one embodiment, the microfibrillating step is conducted in a grinding vessel under wet-grinding conditions. In another embodiment, the microfibrillating step is carried out in a homogenizer. Each of these embodiments is described in greater detail below.

Wet-Grinding Microfibrillation Process

[00167] The grinding may be an attrition grinding process in the presence of a grinding medium, or may be an autogenous grinding process, i.e., one performed in the absence of a grinding medium. By grinding medium is meant a medium other than the at least one inorganic particulate material which is co-ground with the fibrous substrate comprising cellulose.

[00168] The grinding medium, when present, may be of a natural or a synthetic material. The grinding medium may, for example, comprise balls, beads or pellets of any hard mineral, ceramic or metallic material. Such materials may include, for example, alumina, zirconia, zirconium silicate, aluminum silicate or the mullite-rich material which is produced by calcining kaolinitic clay at a temperature in the range of from about 1300°C. to about 1800°C. For example, in some embodiments a Carbolite® grinding medium is used. Alternatively, particles of natural sand of a suitable particle size may be used.

[00169] Generally, the type of and particle size of grinding medium to be selected for use in the invention may be dependent on the properties, such as, e.g., the particle size of, and the chemical composition of, the feed suspension of material to be ground. Preferably, the particulate grinding medium comprises particles having an average diameter in the range of from about 0.1 mm to about 6.0 mm and, more preferably, in the range of from about 0.2 mm to about 4.0 mm. The grinding medium (or media) may be present in an amount up to about

70% by volume of the charge. The grinding media may be present in amount of at least about 10% by volume of the charge, for example, at least about 20% by volume of the charge, or at least about 30% by volume of the charge, or at least about 40% by volume of the charge, or at least about 50% by volume of the charge, or at least about 60% by volume of the charge. [00170] The grinding may be carried out in one or more stages. For example, a coarse inorganic particulate material may be ground in the grinder vessel to a predetermined particle size distribution, after which the fibrous material comprising cellulose is added and the grinding continued until the desired level of microfibrillation has been obtained. The coarse inorganic particulate material used in accordance with an first aspect of this invention initially may have a particle size distribution in which less than about 20% by weight of the particles have an essential spherical diameter (e.s.d) of less than 2 μm, for example, less than about 15% by weight, or less than about 10% by weight of the particles have an e.s.d. of less than 2 μm. In another embodiment, the coarse inorganic particulate material used in accordance with the first aspect of this invention initially may have a particle size distribution, as measured using a Malvern Mastersizer S machine, in which less than about 20% by volume of the particles have an e.s.d of less than 2 μm, for example, less than about 15% by volume, or less than about 10% by volume of the particles have an e.s.d. of less than 2 μm.

[00171] The coarse inorganic particulate material may be wet or dry ground in the absence or presence of a grinding medium. In the case of a wet grinding stage, the coarse inorganic particulate material is preferably ground in an aqueous suspension in the presence of a grinding medium. In such a suspension, the coarse inorganic particulate material may preferably be present in an amount of from about 5% to about 85% by weight of the suspension; more preferably in an amount of from about 20% to about 80% by weight of the suspension. Most preferably, the coarse inorganic particulate material may be present in an amount of about 30% to about 75% by weight of the suspension. As described above, the coarse inorganic particulate material may be ground to a particle size distribution such that at least about 10% by weight of the particles have an e.s.d of less than 2 μm, for example, at least about 20% by weight, or at least about 30% by weight, or at least about 40% by weight, or at least about 50% by weight, or at least about 60% by weight, or at least about 70% by weight, or at least about 80% by weight, or at least about 90% by weight, or at least about 95% by weight, or about 100% by weight of the particles, have an e.s.d of less than 2 μm, after which the cellulose pulp is added and the two components are co-ground to microfibrillate the fibres of the cellulose pulp.

[00172] In another embodiment, the coarse inorganic particulate material is ground to a particle size distribution, as measured using a Malvern Mastersizer S machine such that at least about 10% by volume of the particles have an e.s.d of less than 2 μm, for example, at least about 20% by volume, or at least about 30% by volume or at least about 40% by volume, or at least about 50% by volume, or at least about 60% by volume, or at least about 70% by volume, or at least about 80% by volume, or at least about 90% by volume, or at least about 95% by volume, or about 100% by volume of the particles, have an e.s.d of less than 2 μm, after which the cellulose pulp is added and the two components are co-ground to microfibrillate the fibres of the cellulose pulp.

[00173] In one embodiment, the mean particle size (d ₅₀ ) of the inorganic particulate material is reduced during the co-grinding process. For example, the d ₅₀ of the inorganic particulate material may be reduced by at least about 10% (as measured by a Malvern Mastersizer S machine), for example, the d ₅₀ of the inorganic particulate material may be reduced by at least about 20%, or reduced by at least about 30%, or reduced by at least about 50%, or reduced by at least about 50%, or reduced by at least about 60%, or reduced by at least about 70%, or reduced by at least about 80%, or reduced by at least about 90%. For example, an inorganic particulate material having a d ₅₀ of 2.5 μm prior to co-grinding and a d ₅₀ of 1.5 μm post co- grinding will have been subject to a 40% reduction in particle size. In certain embodiments, the mean particle size of the inorganic particulate material is not significantly reduced during the co-grinding process. By 'not significantly reduced' is meant that the d ₅₀ of the inorganic particulate material is reduced by less than about 10%, for example, the d ₅₀ of the inorganic particulate material is reduced by less than about 5%.

[00174] The fibrous substrate comprising cellulose may be microfibrillated in the presence of at least one inorganic particulate material to obtain microfibrillated cellulose having a d ₅₀ ranging from about 5 μm to about 500 μm, as measured by laser light scattering. The fibrous substrate comprising cellulose may be microfibrillated in the presence of an inorganic particulate material to obtain microfibrillated cellulose having a d ₅₀ of equal to or less than about 400 μm, for example equal to or less than about 300 μm, or equal to or less than about 200 μm or equal to or less than about 150 μm, or equal to or less than about 125 μm, or equal to or less than about 100 μm, or equal to or less than about 90 μm, or equal to or less than about 80 μm, or equal to or less than about 70 μm, or equal to or less than about 60 μm, or equal to or less than about 50 μm, or equal to or less than about 40 μm, or equal to or less than about 30 μm, or equal to or less than about 20 μm, or equal to or less than about 10 μm.

[00175] The fibrous substrate comprising cellulose may be microfibrillated in the presence of an inorganic particulate material to obtain microfibrillated cellulose having a modal fibre particle size ranging from about 0.1-500 μm and a modal inorganic particulate material particle size ranging from 0.25-20 μm. The fibrous substrate comprising cellulose may be microfibrillated in the presence of an inorganic particulate material to obtain microfibrillated cellulose having a modal fibre particle size of at least about 0.5 μm, for example at least about 10 μm, or at least about 50 μm, or at least about 100 μm, or at least about 150 μm, or at least about 200 μm, or at least about 300 μm, or at least about 400 μm.

[00176] The fibrous substrate comprising cellulose may be microfibrillated in the presence of an inorganic particulate material to obtain microfibrillated cellulose having a fibre steepness equal to or greater than about 10, as measured by Malvern. Fibre steepness (i.e. , the steepness of the particle size distribution of the fibres) is determined by the following formula: Steepness=100 X (d ₃₀ /d ₇₀ ).

[00177] The microfibrillated cellulose may have a fibre steepness equal to or less than about 100. The microfibrillated cellulose may have a fibre steepness equal to or less than about 75, or equal to or less than about 50, or equal to or less than about 40, or equal to or less than about 30. The microfibrillated cellulose may have a fibre steepness from about 20 to about 50, or from about 25 to about 40, or from about 25 to about 35, or from about 30 to about 40.

[00178] The grinding is suitably performed in a grinding vessel, such as a tumbling mill (e.g., rod, ball and autogenous), a stirred mill (e.g., SAM or IsaMill), a tower mill, a stirred media detritor (SMD), or a grinding vessel comprising rotating parallel grinding plates between which the feed to be ground is fed.

[00179] In one embodiment, the grinding vessel is a tower mill. The tower mill may comprise a quiescent zone above one or more grinding zones. A quiescent zone is a region located towards the top of the interior of tower mill in which minimal or no grinding takes place and comprises microfibrillated cellulose and inorganic particulate material. The quiescent zone is a region in which particles of the grinding medium sediment down into the one or more grinding zones of the tower mill. [00180] The tower mill may comprise a classifier above one or more grinding zones. In an embodiment, the classifier is top mounted and located adjacent to a quiescent zone. The classifier may be a hydrocyclone.

[00181] The tower mill may comprise a screen above one or more grinding zones. In an embodiment, a screen is located adjacent to a quiescent zone and/or a classifier. The screen may be sized to separate grinding media from the product aqueous suspension comprising microfibrillated cellulose and inorganic particulate material and to enhance grinding media sedimentation.

[00182] In an embodiment, the grinding is performed under plug flow conditions. Under plug flow conditions the flow through the tower is such that there is limited mixing of the grinding materials through the tower. This means that at different points along the length of the tower mill the viscosity of the aqueous environment will vary as the fineness of the microfibrillated cellulose increases. Thus, in effect, the grinding region in the tower mill can be considered to comprise one or more grinding zones which have a characteristic viscosity. A skilled person in the art will understand that there is no sharp boundary between adjacent grinding zones with respect to viscosity.

[00183] In an embodiment, water is added at the top of the mill proximate to the quiescent zone or the classifier or the screen above one or more grinding zones to reduce the viscosity of the aqueous suspension comprising microfibrillated cellulose and inorganic particulate material at those zones in the mill. By diluting the product microfibrillated cellulose and inorganic particulate material composite at this point in the mill it has been found that the prevention of grinding media carry over to the quiescent zone and/or the classifier and/or the screen is improved. Further, the limited mixing through the tower allows for processing at higher solids lower down the tower and dilute at the top with limited backflow of the dilution water back down the tower into the one or more grinding zones. Any suitable amount of water which is effective to dilute the viscosity of the product aqueous suspension comprising microfibrillated cellulose and inorganic particulate material may be added. The water may be added continuously during the grinding process, or at regular intervals, or at irregular intervals.

[00184] In another embodiment, water may be added to one or more grinding zones via one or more water injection points positioned along the length of the tower mill, or each water injection point being located at a position which corresponds to the one or more grinding zones. Advantageously, the ability to add water at various points along the tower allows for further adjustment of the grinding conditions at any or all positions along the mill.

[00185] The tower mill may comprise a vertical impeller shaft equipped with a series of impeller rotor disks throughout its length. The action of the impeller rotor disks creates a series of discrete grinding zones throughout the mill.

[00186] In another embodiment, the grinding is performed in a screened grinder, preferably a stirred media detritor. The screened grinder may comprise one or more screen(s) having a nominal aperture size of at least about 250 μm, for example, the one or more screens may have a nominal aperture size of at least about 300 μm, or at least about 350 μm, or at least about 400 μm, or at least about 450 μm, or at least about 500 μm, or at least about 550 μm, or at least about 600 μm, or at least about 650 μm, or at least about 700 μm, or at least about 750 μm, or at least about 800 μm, or at least about 850 μm, or at or least about 900 μm, or at least about 1000 μm.

[00187] The screen sizes noted immediately above are applicable to the tower mill embodiments described above. [00188] As noted above, the grinding may be performed in the presence of a grinding medium. In an embodiment, the grinding medium is a coarse media comprising particles having an average diameter in the range of from about 1 mm to about 6 mm, for example about 2 mm, or about 3 mm, or about 4 mm, or about 5 mm.

[00189] In another embodiment, the grinding media has a specific gravity of at least about

2.5, for example, at least about 3, or at least about 3.5, or at least about 4.0, or at least about

4.5, or least about 5.0, or at least about 5.5, or at least about 6.0.

[00190] In another embodiment, the grinding media comprises particles having an average diameter in the range of from about 1 mm to about 6 mm and has a specific gravity of at least about 2.5.

[00191] As described above, the grinding medium (or media) may present in an amount up to about 70% by volume of the charge. The grinding media may be present in amount of at least about 10% by volume of the charge, for example, at least about 20% by volume of the charge, or at least about 30% by volume of the charge, or at least about 40% by volume of the charge, or at least about 50% by volume of the charge, or at least about 60% by volume of the charge.

[00192] In one embodiment, the grinding medium is present in amount of about 50% by volume of the charge.

[00193] By ' charge' is meant the composition which is the feed fed to the grinder vessel.

The charge includes of water, grinding media, fibrous substrate comprising cellulose and inorganic particulate material, and any other optional additives as described herein. The use of a relatively coarse and/or dense media has the advantage of improved (i. e. , faster) sediment rates and reduced media carry over through the quiescent zone and/or classifier and/or screen(s). [00194] A further advantage in using relatively coarse grinding media is that the mean particle size (d ₅₀ ) of the inorganic particulate material may not be significantly reduced during the grinding process such that the energy imparted to the grinding system is primarily expended in microfibrillating the fibrous substrate comprising cellulose.

[00195] A further advantage in using relatively coarse screens is that a relatively coarse or dense grinding media can be used in the microfibrillating step. In addition, the use of relatively coarse screens (i.e. , having a nominal aperture of least about 250 um) allows a relatively high solids product to be processed and removed from the grinder, which allows a relatively high solids feed (comprising fibrous substrate comprising cellulose and inorganic particulate material) to be processed in an economically viable process. As discussed below, it has been found that a feed having a high initial solids content is desirable in terms of energy sufficiency. Further, it has also been found that product produced (at a given energy) at lower solids has a coarser particle size distribution.

[00196] Thus, in accordance with one embodiment, the fibrous substrate comprising cellulose and inorganic particulate material are present in the aqueous environment at an initial solids content of at least about 4 wt.%, of which at least about 2% by weight is fibrous substrate comprising cellulose. The initial solids content may be at least about 10 wt. %, or at least about 20 wt. %, or at least about 30 wt. %, or at least about at least 40 wt. %. At least about 5% by weight of the initial solids content may be fibrous substrate comprising cellulose, for example, at least about 10%, or at least about 15%, or at least about 20% by weight of the initial solids content may be fibrous substrate comprising cellulose.

[00197] In another embodiment, the grinding is performed in a cascade of grinding vessels, one or more of which may comprise one or more grinding zones. For example, the fibrous substrate comprising cellulose and the inorganic particulate material may be ground in a cascade of two or more grinding vessels, for example, a cascade of three or more grinding vessels, or a cascade of four or more grinding vessels, or a cascade of five or more grinding vessels, or a cascade of six or more grinding vessels, or a cascade of seven or more grinding vessels, or a cascade of eight or more grinding vessels, or a cascade of nine or more grinding vessels in series, or a cascade comprising up to ten grinding vessels. The cascade of grinding vessels may be operatively linked in series or parallel or a combination of series and parallel. The output from and/or the input to one or more of the grinding vessels in the cascade may be subjected to one or more screening steps and/or one or more classification steps.

[00198] The total energy expended in a microfibrillation process may be apportioned equally across each of the grinding vessels in the cascade. Alternatively, the energy input may vary between some or all of the grinding vessels in the cascade.

[00199] A person skilled in the art will understand that the energy expended per vessel may vary between vessels in the cascade depending on the amount of fibrous substrate being microfibrillated in each vessel, and optionally the speed of grind in each vessel, the duration of grind in each vessel, the type of grinding media in each vessel and the type and amount of inorganic particulate material. The grinding conditions may be varied in each vessel in the cascade in order to control the particle size distribution of both the microfibrillated cellulose and the inorganic particulate material. For example, the grinding media size may be varied between successive vessels in the cascade in order to reduce grinding of the inorganic particulate material and to target grinding of the fibrous substrate comprising cellulose.

[00200] In an embodiment the grinding is performed in a closed circuit. In another embodiment, the grinding is performed in an open circuit. The grinding may be performed in batch mode. The grinding may be performed in a re-circulating batch mode. In another embodiment, the grinding may be performed in a continuous mode, as described elsewhere in this specification.

[00201] As described above, the grinding circuit may include a pre-grinding step in which coarse inorganic particulate ground in a grinder vessel to a predetermined particle size distribution, after which fibrous material comprising cellulose is combined with the pre- ground inorganic particulate material and the grinding continued in the same or different grinding vessel until the desired level of microfibrillation has been obtained.

[00202] As the suspension of material to be ground may be of a relatively high viscosity, a suitable dispersing agent may preferably be added to the suspension prior to grinding. The dispersing agent may be, for example, a water soluble condensed phosphate, polysilicic acid or a salt thereof, or a poly electrolyte, for example a water soluble salt of a poly(acrylic acid) or of a poly(methacrylic acid) having a number average molecular weight not greater than 80,000. The amount of the dispersing agent used would generally be in the range of from 0.1 to 2.0% by weight, based on the weight of the dry inorganic particulate solid material. The suspension may suitably be ground at a temperature in the range of from 4°C. to 100°C.

[00203] Other additives which may be included during the microfibrillation step include: carboxymethyl cellulose, amphoteric carboxymethyl cellulose, oxidising agents, 2, 2, 6, 6- Tetramethylpiperidine-1-oxyl (TEMPO), TEMPO derivatives, and wood degrading enzymes. [00204] The pH of the suspension of material to be ground may be about 7 or greater than about 7 (i.e., basic), for example, the pH of the suspension may be about 8, or about 9, or about 10, or about 11. The pH of the suspension of material to be ground may be less than about 7 (i.e., acidic), for example, the pH of the suspension may be about 6, or about 5, or about 4, or about 3. The pH of the suspension of material to be ground may be adjusted by addition of an appropriate amount of acid or base. Suitable bases included alkali metal hydroxides, such as, for example NaOH. Other suitable bases are sodium carbonate and ammonia. Suitable acids included inorganic acids, such as hydrochloric and sulphuric acid, or organic acids. An exemplary acid is orthophosphoric acid.

[00205] The amount of inorganic particulate material and cellulose pulp in the mixture to be co-ground may vary in a ratio of from about 99.5:0.5 to about 0.5:99.5, based on the dry weight of inorganic particulate material and the amount of dry fibre in the pulp, for example, a ratio of from about 99.5:0.5 to about 50:50 based on the dry weight of inorganic particulate material and the amount of dry fibre in the pulp. For example, the ratio of the amount of inorganic particulate material and dry fibre may be from about 99.5:0.5 to about 70:30. In an embodiment, the ratio of inorganic particulate material to dry fibre is about 80:20, or for example, about 85:15, or about 90:10, or about 91:9, or about 92:8, or about 93:7, or about 94:6, or about 95:5, or about 96:4, or about 97:3, or about 98:2, or about 99:1. In a preferred embodiment, the weight ratio of inorganic particulate material to dry fibre is about 95:5. In another preferred embodiment, the weight ratio of inorganic particulate material to dry fibre is about 90:10. In another preferred embodiment, the weight ratio of inorganic particulate material to dry fibre is about 85:15. In another preferred embodiment, the weight ratio of inorganic particulate material to dry fibre is about 80:20.

[00206] The total energy input in a typical grinding process to obtain the desired aqueous suspension composition may typically be between about 100 and 1500 kWht ^-1 based on the total dry weight of the inorganic particulate filler. The total energy input may be less than about 1000 kWht ^-1 , for example, less than about 800 kWht ^-1 , less than about 600 kWht ^-1 , less than about 500 kWht ^-1 , less than about kWht ^-1 , less than about 300 kWht ^-1 , or less than about 200 kWht ^-1 . As such, the present inventors have surprisingly found that a cellulose pulp can be microfibrillated at relatively low energy input when it is co-ground in the presence of an inorganic particulate material. As will be apparent, the total energy input per tonne of dry fibre in the fibrous substrate comprising cellulose will be less than about 10,000 kWht ^-1 , for example, less than about 9000 kWht ^-1 , or less than about 8000 kWht ^-1 , or less than about 7000 kWht ^-1 , or less than about 6000 kWht ^-1 , or less than about 5000 kWht ^-1 , for example less than about 4000 kWht ^-1 , less than about 3000 kWht ^-1 , less than about 2000 kWht ^-1 , less than about 1500 kWht ^-1 , less than about 1200 kWht ^-1 , less than about 1000 kWht ^-1 , or less than about 800 kWht ^-1 . The total energy input varies depending on the amount of dry fibre in the fibrous substrate being microfibrillated, and optionally the speed of grind and the duration of grind. [00207] In another embodiment, the grinding media comprises particles having an average diameter of about 3 mm and specific gravity of about 2.7.

[00208] In another embodiment, the MFC is manufactured in accordance with the method described in WO-A-2010/131016, which comprises a step of microfibrillating a fibrous substrate comprising cellulose by grinding in the presence of a particulate grinding medium which is to be removed after the completion of grinding. By “microfibrillating” is meant a process in which microfibrils of cellulose are liberated or partially liberated as individual species or as small aggregates as compared to the fibres of the pre-microfibrillated pulp.

Typical cellulose fibres (i.e., pre-microfibrillated pulp) suitable for use in papermaking include larger aggregates of hundreds or thousands of individual cellulose fibrils. By microfibrillating the cellulose, particular characteristics and properties, including the characteristics and properties described herein, are imparted to the MFC and the compositions comprising the MFC.

[00209] The fibrous substrate comprising cellulose (variously referred to herein as “fibrous substrate comprising cellulose,” “cellulose fibres,” “fibrous cellulose feedstock,” “cellulose feedstock” and “cellulose-containing fibres (or fibrous,” etc.) may be derived from recycled pulp or a papermill broke and/or industrial waste, or a paper streams rich in mineral fillers and cellulosic materials from a papermill.

[00210] The cellulose pulp may be beaten (for example in a Valley beater) and/or otherwise refined (for example, processing in a conical or plate refiner) to any predetermined freeness, reported in the art as Canadian standard freeness (CSF) in cm ³ . CSF means a value for the freeness or drainage rate of pulp measured by the rate that a suspension of pulp may be drained, and this test is carried out according to the T 227 cm-09 TAPPI standard. For example, the cellulose pulp may have a Canadian standard freeness of about 10 cm ³ or greater prior to being microfibrillated. The cellulose pulp may have a CSF of about 700 cm ³ or less, for example, equal to or less than about 650 cm ³ , or equal to or less than about 600 cm ³ , or equal to or less than about 550 cm ³ , or equal to or less than about 500 cm ³ , or equal to or less than about 450 cm ³ , or equal to or less than about 400 cm ³ , or equal to or less than about 350 cm ³ , or equal to or less than about 300 cm ³ , or equal to or less than about 250 cm ³ , or equal to or less than about 200 cm ³ , or equal to or less than about 150 cm ³ , or equal to or less than about 100 cm ³ , or equal to or less than about 50 cm ³ . The cellulose pulp may have a CSF of about 20 to about 700. The cellulose pulp may then be dewatered by methods well known in the art, for example, the pulp may be filtered through a screen in order to obtain a wet sheet comprising at least about 10% solids, for example at least about 15% solids, or at least about 20% solids, or at least about 30% solids, or at least about 40% solids or at least 50% solids. The pulp may be utilized in an unrefined state, that is to say, without being beaten or dewatered, or otherwise refined.

[00211] In another embodiment, the microfibrillated cellulose is prepared in accordance with a method comprising a step ofmicrofibrillating a fibrous substrate comprising cellulose in an aqueous environment by grinding in the presence of a grinding medium which is to be removed after the completion of grinding, wherein the grinding is performed in a tower mill or a screened grinder, and wherein the grinding is carried out in the absence of grindable inorganic particulate material.

[00212] A grindable inorganic particulate material is a material which would be ground in the presence of the grinding medium.

[00213] The particulate grinding medium may be of a natural or a synthetic material. The grinding medium may, for example, comprise balls, beads or pellets of any hard mineral, ceramic or metallic material. Such materials may include, for example, alumina, zirconia, zirconium silicate, aluminium silicate or the mullite-rich material which is produced by calcining kaolinitic clay at a temperature in the range of from about 1300°C to about 1800°C. For example, in some embodiments a Carbolite® grinding media is preferred. Alternatively, particles of natural sand of a suitable particle size may be used.

[00214] Generally, the type of and particle size of grinding medium to be selected for use in the invention may be dependent on the properties, such as, e.g., the particle size of, and the chemical composition of, the feed suspension of material to be ground. Preferably, the particulate grinding medium comprises particles having an average diameter in the range of from about 0.5 mm to about 6 mm. In one embodiment, the particles have an average diameter of at least about 3 mm.

[00215] The grinding medium may comprise particles having a specific gravity of at least about 2.5. The grinding medium may comprise particles have a specific gravity of at least about 3, or least about 4, or least about 5, or at least about 6.

[00216] The grinding medium (or media) may be present in an amount up to about 70% by volume of the charge. The grinding media may be present in amount of at least about 10% by volume of the charge, for example, at least about 20 % by volume of the charge, or at least about 30% by volume of the charge, or at least about 40 % by volume of the charge, or at least about 50% by volume of the charge, or at least about 60 % by volume of the charge.

[00217] The fibrous substrate comprising cellulose may be microfibrillated to obtain microfibrillated cellulose having a d ₅₀ ranging from about 5 to μm about 500 μm, as measured by laser light scattering. The fibrous substrate comprising cellulose may be microfibrillated to obtain microfibrillated cellulose having a d ₅₀ of equal to or less than about 400 μm, for example equal to or less than about 300 μm, or equal to or less than about 200 μm, or equal to or less than about 150 μm, or equal to or less than about 125 μm, or equal to or less than about 100 μm, or equal to or less than about 90 μm, or equal to or less than about 80 μm, or equal to or less than about 70 μm, or equal to or less than about 60 μm, or equal to or less than about 50 μm, or equal to or less than about 40 μm, or equal to or less than about 30 μm, or equal to or less than about 20 μm, or equal to or less than about 10 μm.

[00218] The fibrous substrate comprising cellulose may be microfibrillated to obtain microfibrillated cellulose having a modal fibre particle size ranging from about 0.1-500 μm. The fibrous substrate comprising cellulose may be microfibrillated in the presence to obtain microfibrillated cellulose having a modal fibre particle size of at least about 0.5 μm, for example at least about 10 μm, or at least about 50 μm, or at least about 100 μm, or at least about 150 μm, or at least about 200 μm, or at least about 300 μm, or at least about 400 μm. [00219] The fibrous substrate comprising cellulose may be microfibrillated to obtain microfibrillated cellulose having a fibre steepness equal to or greater than about 10, as measured by Malvern. Fibre steepness (i.e., the steepness of the particle size distribution of the fibres) is determined by the following formula:

Steepness = 100 x (d ₃₀ /d ₇₀ ) [00220] The microfibrillated cellulose may have a fibre steepness equal to or less than about 100. Tire microfibrillated cellulose may have a fibre steepness equal to or less than about 75, or equal to or less than about 50, or equal to or less than about 40, or equal to or less than about 30. The microfibrillated cellulose may have a fibre steepness from about 20 to about 50, or from about 25 to about 40, or from about 25 to about 35, or from about 30 to about 40. In an embodiment, a preferred steepness range is about 20 to about 50.

[00221] Calculation of fibre steepness of MFC fibres and inorganic particulate material is well known in the art. For example, a sample of co-ground slurry sufficient to give 5 g dry material is weighed into a beaker, diluted to 60g with deionised water, and mixed with 5 cm3 of a solution of 1.0 wt% sodium carbonate and 0.5 wt% sodium hexametaphosphate. Further deionised water is added with stirring to a final slurry weight of 80 g. The slurry is then added in 1 cm ³ aliquots to water in the sample preparation unit attached to the Mastersizer S (or Mastersizer Insitec or other comparable apparatus) until the optimum level of obscuration is displayed (normally 10 - 15%). The light scattering analysis procedure is then carried out. The instrument range selected was 300RF : 0.05-900, and the beam length set to 2.4 mm. For co- ground samples containing calcium carbonate and fibre the refractive index for calcium carbonate (1.596) is used. For co-ground samples of kaolin and fibre the RI for kaolin (1.5295) is used. The particle size distribution is calculated from Mie theory and gives the output as a differential volume based distribution. The presence of two distinct peaks is interpreted as arising from the mineral (finer peak) and fibre (coarser peak).

[00222] The finer mineral peak is fitted to the measured data points and subtracted mathematically from the distribution to leave the fibre peak, which is converted to a cumulative distribution. Similarly, the fibre peak is subtracted mathematically from the original distribution to leave the mineral peak, which is also converted to a cumulative distribution. Both these cumulative curves may then be used to calculate the mean particle size (d5 o) and the steepness of the distribution (d30/d ₇₀ x 100). The differential curve may be used to find the modal particle size for both the mineral and fibre fractions

[00223] In one embodiment, the grinding vessel is a tower mill. The tower mill may comprise a quiescent zone above one or more grinding zones. A quiescent zone is a region located towards the top of the interior of a tower mill in which minimal or no grinding takes place and comprises microfibrillated cellulose and inorganic particulate material. The quiescent zone is a region in which particles of the grinding medium sediment down into the one or more grinding zones of the tower mill.

[00224] The tower mill may comprise a classifier above one or more grinding zones. In an embodiment, the classifier is top mounted and located adjacent to a quiescent zone. The classifier may be a hydrocyclone.

[00225] The tower mill may comprise a screen above one or more grind zones. In an embodiment, a screen is located adjacent to a quiescent zone and/or a classifier. The screen may be sized to separate grinding media from the product aqueous suspension comprising microfibrillated cellulose and to enhance grinding media sedimentation.

[00226] In an embodiment, the grinding is performed under plug flow conditions. Under plug flow conditions the flow through the tower is such that there is limited mixing of the grinding materials through the tower. This means that at different points along the length of the tower mill the viscosity of the aqueous environment will vary as the fineness of the microfibrillated cellulose increases. Thus, in effect, the grinding region in the tower mill can be considered to comprise one or more grinding zones which have a characteristic viscosity. A skilled person in the art will understand that there is no sharp boundary between adjacent grinding zones with respect to viscosity. [00227] In an embodiment, water is added at the top of the mill proximate to the quiescent zone or the classifier or the screen above one or more grinding zones to reduce the viscosity of the aqueous suspension comprising microfibrillated cellulose at those zones in the mill. By diluting the product microfibrillated cellulose at this point in the mill it has been found that the prevention of grinding media carry over to the quiescent zone and/or the classifier and/or the screen is improved. Further, the limited mixing through the tower allows for processing at higher solids lower down the lower and dilute at the top with limited backfl ow of the dilution water back down the tower into the one or more grinding zones. Any suitable amount of water which is effective to dilute the viscosity' of the product aqueous suspension comprising microfibrillated cellulose may be added. The water may be added continuously during the grinding process, or at regular intervals, or at irregular intervals.

[00228] In another embodiment, water may be added to one or more grinding zones via one or more water injection points positioned along the length of the tower mill, the or each water injection point being located at a position which corresponds to the one or more grinding zones. Advantageously, the ability to add water at various points along the tower allows for further adjustment of the grinding conditions at any or all positions along the mill.

[00229] The tower mill may comprise a vertical impeller shaft equipped with a series of impeller rotor disks throughout its length. The action of the impeller rotor disks creates a series of discrete grinding zones throughout the mill.

[00230] In another embodiment, the grinding is performed in a screened grinder, preferably a stirred media detritor. The screened grinder may comprise one or more screen(s) having a nominal aperture size of at least about 250 μm, for example, the one or more screens may have a nominal aperture size of at least about 300 μm, or at least about 350μm, or at least about 400 μm, or at least about 450 μm, or at least about 500 μm, or at least about 550 μm, or at least about 600 μm, or at least about 650 μm, or at least about 700 μm, or at least about 750 μm, or at least about 800 μm, or at least about 850 μm, or at or least about 900 μm, or at least about 1000 μm, or at least about 1 ,250 μm, or at least about 1,500 μm.

[00231] The screen sizes noted immediately above are applicable to the tower mill embodiments described above.

[00232] As noted above, the grinding is performed in the presence of a grinding medium. In an embodiment, the grinding medium is a coarse media comprising particles having an average diameter in the range of from about 1 mm to about 6 mm, for example about 2 mm, or about 3 mm, or about 4 mm, or about 5 mm.

[00233] In another embodiment, the grinding media has a specific gravity of at least about

2.5, for example, at least about 3, or at least about 3.5, or at least about 4.0, or at least about

4.5, or least about 5.0, or at least about 5.5, or at least about 6.0.

[00234] As described above, the grinding medium (or media) may be in an amount up to about 70% by volume of the charge. The grinding media may be present in amount of at least about 10% by volume of the charge, for example, at least about 20 % by volume of the charge, or at least about 30% by volume of the charge, or at least about 40 % by volume of the charge, or at least about 50% by volume of the charge, or at least about 60 % by volume of the charge.

[00235] In one embodiment, the grinding medium is present in amount of about 50% by volume of the charge.

[00236] By 'charge' is meant the composition which is the feed fed to the grinder vessel. The charge includes water, grinding media, the fibrous substrate comprising cellulose and any other optional additives (other than as described herein). [00237] The use of a relatively coarse and/or dense media has the advantage of improved (i.e,, faster) sediment rates and reduced media carry over through the quiescent zone and/or classifier and/or screen(s).

[00238] A further advantage in using relatively coarse screens is that a relatively coarse or dense grinding media can be used in the microfibrillating step. In addition, the use of relatively coarse screens (i.e., having a nominal aperture of least about 250 urn) allows a relatively high solids product to be processed and removed from the grinder, which allows a relatively high solids feed (comprising fibrous substrate comprising cellulose and inorganic particulate material) to be processed in an economically viable process. As discussed below, it has been found that a feed having a high initial solids content is desirable in terms of energy sufficiency. Further, it has also been found that product produced (at a given energy) at lower solids has a coarser particle size distribution.

[00239] In accordance with one embodiment, the fibrous substrate comprising cellulose is present in the aqueous environment at an initial solids content of at least about 1 wt. %. The fibrous substrate comprising cellulose may be present in the aqueous environment at an initial solids content of at least about 2 wt. %, for example at least about 3 wt. %, or at least about at least 4 wt. %. Typically the initial solids content will be no more than about 10 wt. %.

[00240] In another embodiment, the grinding is performed in a cascade of grinding vessels, one or more of which may comprise one or more grinding zones. For example, the fibrous substrate comprising cellulose may be ground in a cascade of two or more grinding vessels, for example, a cascade of three or more grinding vessels, or a cascade of four or more grinding vessels, or a cascade of five or more grinding vessels, or a cascade of six or more grinding vessels, or a cascade of seven or more grinding vessels, or a cascade of eight or more grinding vessel s, or a cascade of nine or more grinding vessel s in series, or a cascade comprising up to ten grinding vessels. The cascade of grinding vessels may be operatively inked in series or parallel or a combination of series and parallel. The output from and/or the input to one or more of the grinding vessels in the cascade may be subjected to one or more screening steps and/or one or more classification steps.

[00241] The total energy expended in a microfibrillation process may be apportioned equally across each of the grinding vessels in the cascade. Alternatively, the energy input may vary between some or all of the grinding vessels in the cascade.

[00242] A person skilled in the art will understand that the energy expended per vessel may vary between vessels in the cascade depending on the amount of fibrous substrate being microfibrillated in each vessel, and optionally the speed of grind in each vessel, the duration of grind in each vessel and the type of grinding media in each vessel. The grinding conditions may be varied in each vessel in the cascade in order to control the particle size distribution of the microfibrillated cellulose.

[00243] In an embodiment the grinding is performed in a closed circuit. In another embodiment, the grinding is performed in an open circuit.

[00244] As the suspension of material to be ground may be of a relatively high viscosity, a suitable dispersing agent may preferably be added to the suspension prior to grinding. The dispersing agent may be, for example, a water soluble condensed phosphate, polysilicic acid or a salt thereof, or a poly electrolyte, for example a water soluble salt of a poly(acrylic acid) or of a poly(methacrylic acid) having a number average molecular weight not greater than 80,000. The amount of the dispersing agent used would generally be in the range of from 0.1 to 2.0% by weight, based on the weight of the dry' inorganic particulate solid material. The suspension may suitably be ground at a temperature in the range of from 4°C to 100°C. [00245] Other additives which may be included during the microfibrillation step include: carboxy methylcellulose, amphoteric carboxymethylcellulose, oxidising agents, 2, 2,6,6- Tetramethylpiperidine-1-oxyl (TEMPO), TEMPO derivatives, and wood degrading enzymes. [00246] The pH of the suspension of material to be ground may be about 7 or greater than about 7 (i.e., basic), for example, the pH of the suspension may be about 8, or about 9, or about 10, or about 11. The pH of the suspension of material to be ground may be less than about 7 (i.e., acidic), for example, the pH of the suspension may be about 6, or about 5, or about 4, or about 3. The pH of the suspension of material to be ground may be adjusted by addition of an appropriate amount of acid or base. Suitable bases included alkali metal hydroxides, such as, for example NaOH. Other suitable bases are sodium carbonate and ammonia. Suitable acids included inorganic acids, such as hydrochloric and sulphuric acid, or organic acids. An exemplary acid is orthophosphoric acid.

[00247] The total energy input in a typical grinding process to obtain the desired aqueous suspension composition may typically be between about 100 and 1500 kWh ⁴ based on the total dry weight of the inorganic particulate filler. The total energy input may be less than about 1000 kWht ^-1 , for example, less than about 800 kWht ^-1 less than about 600 kWht ^-1 A less than about 500 kWht ^-1 , less than about 400 kWht ^-1 less than about 300 kWht ^-1 A or less than about 200 kWht ^-1 As such, the present inventors have surprisingly found that a cellulose pulp can be microfibrillated at relatively low energy input when it is co-ground in the presence of an inorganic particulate material. As will be apparent, the total energy input per tonne of dry fibre in the fibrous substrate comprising cellulose will be less than about 10,000 kWht ^-1 , for example, less than about 9000 kWht ^-1 or less than about 8000 kWht ^-1 , or less than about

7000 kWht ^-1 , or less than about 6000 kWht ^-1 , or less than about 5000 kWht ^-1 for example less than about 4000 kWht ^-1 , less than about 3000 kWht ^-1 , less than about 2,000 kWht ^-1 , less than about 1500 kWht ^-1 less than about 1200 kWht ^-1 , less than about 1000 kWht ^-1 or less than about 800 kWht ^-1 . The total energy input varies depending on the amount of dry fibre in the fibrous substrate being microfibrillated, and optionally the speed of grind and the duration of grind.

[00248] Various aspects of the invention are described in further detail in the following subsections. The use of subsections is not meant to limit the invention. Each subsection may apply to any aspect of the invention. In this application, the use of "or" means "and/or" unless stated otherwise.

[00249] MFC may be produced in a continuous or batch mode. MFC is an aqueous suspension mixture of microfibrillated cellulose and inorganic particulate material. In an embodiment, MFC is prepared by co-grinding a low solids aqueous suspension of cellulose wood pulp in the presence of inorganic particulate material particles in a wet vertically stirred media mill. The mineral particles act as grinding aids and facilitate the cost-effective fibrillation of pulp fibers to microfibrils in a process analogous to pulp refining.

[00250] The inorganic particulate material used is a standard paper filler, often calcium carbonate or kaolin. Most processes will use kaolin, ground calcium carbonate or precipitated calcium carbonate. The inorganic particulate material will be in aqueous slurry form.

[00251] The cellulose used is typically unrefined Kraft or sulphite pulp from a paper mill’s pulp source (>99% cellulose) or recycled pulp from paper and board recycling activities. The pulp is received from the paper mill as an aqueous slurry usually at approximately 4-5 wt.% solids. The water used will be from the mill’s process streams or in some cases council (city) water. The ceramic grinding media are typically 3mm diameter beads made from calcined kaolin. In some cases when recycled pulp is used, the pulp will already contain some inorganic particulate material.

[00252] In an illustrative recipe: Kraft pulp at approximately 4% solids and hydrous kaolin at approximately 66% solids or calcium carbonate slurry at approximately 75% solids and water are added to the grinder continuously. The grinder is loaded with 3mm diameter mullite grinding media such that approximately 50% of the total charge volume is occupied by the media (total charge volume = volume occupied by mullite + pulp + kaolin +water). The throughput is controlled such that the pulp and mineral mixture is co-ground for an optimised period. Typically, this optimum period corresponds to the develoμment of maximum viscosity and tensile properties. Typically, between approximately 1500 - 5000 kWhr/ dry tonne of MFC is applied. The temperature in the grinder reaches about 65 degrees centigrade during the grind. The MFC product is in aqueous slurry form.

[00253] In some cases, rather than running continuously, the same process is operated batchwise. In this case, the ingredients are added at the start of a batch, then the grinders are run for an allocated time such that 1500-5000 kWhr/dry tonne of MFC is applied and then at the end of the batch further water is added and the product is discharged before the process being repeated.

[00254] In some cases, where inorganic particulate material cannot be tolerated in an end use application, the above processes are conducted without any added inorganic particulate material.

[00255] The above MFC product which results from the grinding and screening process contains agglomerates which reduce performance and can cause blockages if subjected to very fine screening. These agglomerates may be reduced by the use of a homogeniser. [00256] In some cases some of the water associated with the MFC product is removed to lower transportation costs. This is achieved by use of dewatering via a belt press and/or drying using a hot air dryer or by other means known in the art. When dewatered and dried products are prepared, a biocide is sometimes added to increase shelf life and protect the product from decomposition. The biocide is mixed into the MFC, for example, using a plough shear mixer. The dewatered and partially dried products are usually shipped in bulk bags.

[00257] The biocides used are DBNPA (2,2-dibromo-3-nitrilopropionamide), and CMIT/ MIT (5-chloro-2-methyl-2H-isothiazol-3-one/2-methyl-2Hi sothiazol-3-one (CMIT/MIT) or for the partially dried product and OIT (2-octyl-2H-isothiazol-3-one).

[00258] The continuous production process is a pass- through process with cellulose, inorganic particulate material and water being sourced from the mill and returned to the mill after processing.

[00259] Parameters that may be used to control production are product d ₅₀ , as measured by laser light scattering and either viscosity or tensile properties, for example, the FLT tensile index described elsewhere in this specification.

[00260] Various aspects of the invention are described in further detail in the following subsections. The use of subsections is not meant to limit the invention. Each subsection may apply to any aspect of the invention. In this application, the use of "or" means "and/or" unless stated otherwise.

Microporous Inorganic Particulate Material Composites

[00261] Some types of filler, such as calcined clays and scalenohedral and aragonite precipitated calcium carbonates (PCC), consist of aggregates of particles with open porous structures (i.e. , these are examples of microporous inorganic particulate materials). Calcined clays are described in U.S. Patent No. 3,586,523, which is hereby incorporated in by reference in its entirety. Such calcined kaolin clays are substantially anhydrous, amorphous aluminum silicates which are obtained by calcining a specific type of kaolin clay, for example, hard sedimentary kaolin clay.

[00262] Precipitated calcium carbonate (PCC) in clustered form is known in the art as disclosed in U.S. Patent No. 5,695,733, which is hereby incorporated by reference in its entirety. The PCC is produced in a unique clustered form having a substantial proportion of particles having a prismatic morphology. By controlling the solution environment utilized to produce PCC, i.e., the slaking of lime (calcium oxide), temperature of carbonation and the rate of introduction of carbon dioxide, either calcite, aragonite, or vaterite are produced.

Again, depending upon the process conditions calcite may have either prismatic, scalenohedral or rhombohedral crystal forms.

[00263] Other examples of microporous inorganic particulate materials include chemically aggregated filler materials. Examples of such chemically aggregated fillers may be found in U.S. Patent No. 4,072,537, which is incorporated herein in its entirety. Such microporous inorganic particulate materials comprise a composite silicate material comprising a clay component and a metal silicate component. The clay component is typically kaolin clay or kaolinite and the metal silicate material is typically a water soluble alkali metal silicate, for example sodium silicate.

[00264] As described in the ‘537 patent, preferred method for preparing the composite pigment comprises the steps of, (a) forming an aqueous suspension of a clay pigment, (b) blending into the clay slurry a quantity of a salt such as calcium chloride, (c) metering into the slurry of clay and salt at high shear a quantity of a silicate component such as sodium silicate, and, optionally, (d) adjusting the pH of the slurry with the addition of alum to a pH no lower than pH 4, before (e) filtering and washing the precipitated product to remove any soluble salts. Such microporous composite silicate material is either used directly in a papermaking process or dried and used later. Additional microporous inorganic particulate material include materials such as diatomaceous earth and expanded perlite.

[00265] All of foregoing materials consist of particles which contain rigid internal void spaces that persist through paper pressing and drying, and should also remain largely intact after calendering.

[00266] Scalenohedral PCC, calcined clays and chemically aggregated fillers achieve this structure by forming open aggregates of smaller particles and bonding the particles strongly where they contact each other. Diatomaceous earth consists of particles which naturally contain pores. Milled expanded perlite consists of fragments of micron-sized glass bubbles. Thus, microporous inorganic particulate materials comprise discrete particles or aggregates of particles with outer dimensions of several microns, which contain void spaces within the volume defined by the outer dimensions and which are several time smaller than said outer dimensions. Collectively, the foregoing inorganic particulate material are designated herein as “microporous inorganic particulate materials” for the purpose of the present invention.

[00267] When used in paper, these microporous inorganic particulate materials have a much larger effect per unit mass of filler on the spacing of the fibres than solid filler particles. This makes them more detrimental to paper strength, but generates increased light scattering which is beneficial to optical properties.

[00268] Another effect of inorganic particulate materials is always to increase sheet porosity (air permeability), which is a significant disadvantage in printing and converting processes.

The effective density of the microporous inorganic particulate materials is also lower than that of solid fillers, and the combination of these effects can lead to an increase in sheet bulk and thickness as fibre is substituted for filler.

[00269] For scalenohedral PCC (an example of microporous inorganic particulate material), the effect of agglomeration on strength can be offset somewhat by controlling the particle size distribution to a narrow range (thus eliminating ultrafine particles which are very detrimental to paper strength) and using a larger median particle size than is optimum for light scattering. However, if the particle or agglomerate size is too large, then light scattering efficiency is lost.

[00270] In an aspect of the present disclosure, the microporous inorganic particulate material composite has a median particle size (d ₅₀ ) less than about 10 μm and greater than about 3 μm, or from about 3 μm to about 6 μm.

In an aspect of the present disclosure, the microporous inorganic particulate material composite, the d ₅₀ of the microporous mineral composites is substantially larger compared to the d50 of an unagglomerated mixture of the same constituents used to form the microporous mineral composites.

[00271] The microporous inorganic particulate material and microfibrillated cellulose composite can be provided in the form of a powder, although they are preferably added in the form of a suspension, such as an aqueous suspension. In this case, the solids content of the suspension is not critical as long as it is a pumpable liquid.

[00272] For the determination of the weight median particle size d ₅₀ , for particles having a d ₅₀ greater than 0.5 μm, a Sedigraph 5100 device from the company Micromeritics, USA may be used. The measurement may be performed in an aqueous solution of 0.1 wt-% Na ₄ P ₂ O ₇ . The samples may be dispersed using a high-speed stirrer and ultrasound. For the determination of the volume median particle size for particles having a d ₅₀ ≤ 500 nm, a Malvern Mastersizer from the company Malvern, UK may be used. The measurement may be performed in an aqueous solution of 0.1 wt% Na ₄ P ₂ O ₇ The samples may be dispersed using a high-speed stirrer and ultrasound. The Sedigraph 5100 provides measurements and a plot of the cumulative percentage by weight of particles having a size, referred to in the art as the “equivalent spherical diameter,” or “esd.” Alternatively, the particle size characteristics of microporous mineral composites may be measured by a Malvern Mastersizer or Microtrac laser particle size distribution analyzer utilizing the suppliers instructions.

[00273] In an aspect of the present disclosure, the ratio of the first inorganic particulate material to the second inorganic particulate material may range from about 10:90 to about 90:10 by weight, for example, from about 20:80 to about 80:20 by weight, about 25:75 to 75:25 by weight, about 40:60 to about 60:40 by weight, or about 50:50 by weight.

Binders

[00274] In an aspect of the present disclosure, a binder may be used to facilitate agglomeration of the second microporous inorganic particulate material to the first microporous inorganic particulate material, and/or to the microfibrillated cellulose. For example, in some embodiments, the binder may be an alkali silica binder.

[00275] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the binder may include at least one of an inorganic binder or an organic binder. The binder may also improve the adhesion and mechanical strength between components of the microporous mineral composites.

[00276] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the binder may include an inorganic binder, such as an alkali metal silicate.

[00277] In an embodiment of the foregoing aspects and embodiments of the present disclosure, a blend of inorganic particulate materials may be contacted with a binder solution by mixing the binder solution with the blend of inorganic particulate materials.

[00278] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the mixing may include agitation.

[00279] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the blend of the first and second microporous inorganic particulate materials and the binder solution is mixed sufficiently to at least substantially uniformly distribute the binder solution among the agglomeration points of contact of the first and/or first and second inorganic particulate materials.

[00280] In an embodiment of the foregoing aspects and embodiments of the present disclosure, a blend of the first and second microporous inorganic particulate materials and the binder solution may be mixed with sufficient agitation to at least substantially uniformly distribute the binder solution among the agglomeration points of contact of the blend of first and second inorganic particulate materials without damaging the structure of the first or second inorganic particulate materials.

[00281] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the contacting may include low-shear mixing.

[00282] In an embodiment of the foregoing aspects and embodiments of the present disclosure, mixing may occur at about room temperature (i.e., from about 20° C. to about 23° C ). In other embodiments, mixing may occur at a temperature ranging from about 20° C. to about 50° C. In further embodiments, mixing may occur at a temperature ranging from about 30° C. to about 45° C. In still other embodiments, mixing may occur at a temperature of from about 35° C. to about 40° C. [00283] In an embodiment of the foregoing aspects and embodiments of the present disclosure, contacting may include spraying the blend of first and/or first and second microporous inorganic particulate materials with a binder solution. In some embodiments, the spraying may be intermittent. In other embodiments, the spraying may be continuous. In further embodiments, spraying includes mixing the blend of the first and second microporous inorganic particulate materials while spraying with a binder solution, for example, to expose different agglomeration points of contacts to the spray. In some embodiments, such mixing may be intermittent. In other embodiments, such mixing may be continuous.

[00284] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the binder may be present in the binder solution in an amount less than about 40% by weight, relative to the weight of the binder solution. In some embodiments, the binder may range from about 1% to about 10% by weight. In further embodiments, the binder may range from about 1% to about 5% by weight.

[00285] In an embodiment of the foregoing aspects and embodiments of the present disclosure, the binder facilitates agglomeration of the second microporous inorganic particulate material to the first microporous inorganic particulate material. According to some embodiments, the second microporous inorganic particulate material has a smaller diameter than the first microporous inorganic particulate material.

[00286] In an aspect of the present disclosure, the microporous inorganic particulate material and microfibrillated cellulose composite may be associated with dispersing agents such as those selected from the group comprising homopolymers or copolymers of poly carboxylic acids and/or their salts or derivatives such as esters based on, e.g., acrylic acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid; e.g. acryl amide or acrylic esters such as methylmethacrylate, or mixtures thereof; alkali polyphosphates, phosphonic-, citric- and tartaric acids and the salts or esters thereof; or mixtures thereof.

[00287] In an aspect of the present disclosure, the combination of microfibrillated cellulose and microporous inorganic particulate material can be carried out by adding the microporous inorganic particulate material to the MFC in one or several steps.

[00288] In an aspect of the present disclosure, the combination of microporous inorganic particulate material can be added to the MFC in one or several steps. The microfibrillated cellulose and microporous inorganic particulate material can be added entirely or in portions after the fibrillating step.

[00289] In an aspect of the present disclosure, the weight ratio of MFC to microporous inorganic particulate material on a dry weight basis is from 1:33 to 10:1, more preferably 1:10 to 7:1, even more preferably 1:5 to 5:1, typically 1:3 to 3:1, especially 1:2 to 2:1 and most preferably 1:1.5 to 1.5:1, e.g. 1:1.

[00290] In an aspect of the present disclosure, the total content of microporous inorganic particulate material is present in an amount of from 10 wt-% to 95 wt-%, preferably from 15 wt-% to 90 wt-%, more preferably from 20 to 75 wt-%, even more preferably from 25 wt-% to 67 wt-%, especially from 33 to 50 wt-% on a dry weight basis of the composite material.

Precipitated Calcium Carbonate

[00178] Precipitated calcium carbonate (PCC) may be used as the source of particulate calcium carbonate in the present invention, and may be produced by any of the known methods available in the art. TAPPI Monograph Series No 30, 'Paper Coating Pigments", pages 34-35 describes the three main commercial processes for preparing precipitated calcium carbonate which is suitable for use in preparing products for use in the paper industry, but may also be used in the practice of the present invention. In all three processes, a calcium carbonate feed material, such as limestone, is first calcined to produce quicklime, and the quicklime is then slaked in water to yield calcium hydroxide or milk of lime. In the first process, the milk of lime is directly carbonated with carbon dioxide gas. This process has the advantage that no by-product is formed, and it is relatively easy to control the properties and purity of the calcium carbonate product. In the second process the milk of lime is contacted with soda ash to produce, by double decomposition, a precipitate of calcium carbonate and a solution of sodium hydroxide. The sodium hydroxide may be substantially completely separated from the calcium carbonate if this process is used commercially. In the third main commercial process the milk of lime is first contacted with ammonium chloride to give a calcium chloride solution and ammonia gas. The calcium chloride solution is then contacted with soda ash to produce by double decomposition precipitated calcium carbonate and a solution of sodium chloride. The crystals can be produced in a variety of different shapes and sizes, depending on the specific reaction process that is used. The three main forms of PCC crystals are aragonite, rhombohedral and scalenohedral, all of which are suitable for use in the present invention, including mixtures thereof.

[00179] In certain embodiments, the PCC may be formed during the process of producing microfibrillated cellulose.

[00180] Wet grinding of calcium carbonate involves the formation of an aqueous suspension of the calcium carbonate which may then be ground, optionally in the presence of a suitable dispersing agent. Reference may be made to, for example, EP-A-614948 (the contents of which are incorporated by reference in their entirety) for more information regarding the wet grinding of calcium carbonate. [00181] In some circumstances, minor additions of other minerals may be included, for example, one or more of kaolin, calcined kaolin, wollastonite, bauxite, talc or mica, could also be present.

[00182] Examples

[00183] Example 1. Use of Coarse Scalenohedral PCC and FiberLean MFC for Maintaining Bulk and Stiffness When Increasing the Filler Content.

[00184] The furnish was prepared from 70% hardwood (Eucalyptus, ex. UPM Uruguay) and 30% softwood (BOTNIA RMA90 Pine, ex. Metsa) co-refined to 450 CSF (28.5 °S.R.).

[00185] The study design targeted 80 g/m ² UWF paper with a starting filler content of 19% arising from GCC (60% <2 μm) addition.

[00186] The MFC product used was 50% POP MFCslurry comprised of NBSK Botnia RMA90 and GCC mineral (60% < 2μm).

[00187] A retention aid was added at 0.12% based on dry sheet weight. The retention aid was cationic polyacrylamide (Percol 292NS, ex. BASF). The white water was re-circulated during sheet-forming (in that the white- water from each sheet was used to form the subsequent sheets in the trial point series to ensure retention equilibrium was reached with each formulation). Further details on the sheet forming methodology are shown in the Appendix

[00188] The results of Example 1 are summarized in Table 1. Table 1: Summary of results when using PCC with MFC to restore Bulk and Stiffness when increasing the filler content.

[00189] N.B.: The furnish (70% Eucalyptus / 30% Pine) represent 100% of the pulp furnish, which was then replaced in the proportions shown by filler and MFC in terms of overall mass per sheet.

[00190] These results indicate:

[00191] Increase of filler content from 20% to 30% using standard GCC (IC60, median size

1.6 μm) with 3% MFC gives minor reduction in strength but significant loss of Bulk and Stiffness.

[00192] Increased MFC dose would result in greater Bulk loss.

Increase of filler content from 20% to 30% using coarse PCC (median size 3.1 μm) gives very high Porosity and low strength.

[00193] Combination of 30% PCC and 4% MFC gives high Bulk, acceptable Porosity and strength and comparable Stiffness with 20% GCC filled paper

[00194] Taken together the Examples demonstrate that:

[00195] MFC addition improves mechanical properties, Opacity, Porosity and Roughness. In exchange for these improvements, several possibilities are presented: [00196] Furnish adjustments: Reduced long fibre or increased CTMP contents (adjusting short fibre content proportionately).

[00197] Change of filler type used and increasing the filler content.

[00198] Both possibilities present potential cost savings.

[00199] The use of MFC also reduces the Bulk, which in turn leads to a detriment to

Stiffness. Furthermore, using MFC to increase the filler level can lead to a greater detriment to Stiffness.

[00200] These Bulk/Stiffhess losses can be offset by:

[00201] Switching to a coarser/bulkier filler.

[00202] Reducing the long fibre content in the furnish.

[00203] Increasing the mechanical pulp content in the furnish.

[00204] Optimisation of these various levers when using MFC can maximise cost savings and overall paper properties

[00205] All paper tests were conducted in accordance with the following TAPPI standards:

[00206] Internal bond strength (Scott Bond): T 569

[00207] Tensile Properties: T494

[00208] Bendtsen Porosity: T460

[00209] Thickness (Caliper for Bulk calculations): T411

[00210] Basis weight: T410

[00211] Opacity: T425

[00212] Ash content: T413 and T211

[00213] Tensile Strength

[00214] Burst Strength: T403

[00215] Tear strength [00216] Tensile strength in the ‘Z’ direction (perpendicular to the plane of the paper) [00217] Bending Stiffness: T535 [00218] Bulk or thickness.

[00219] Roughness: T555

[00220] Sheet Preparation

[00221] All handsheets were prepared on a Rapid Kothen sheetformer according to TAPPI standard T205. In order to ensure very high overall retention of all components of the furnishes used to make the sheets, whitewater was recirculated after the formation of each sheet and used in the dilution of the furnish used to make the next sheet. The first 5 sheets of each composition were discarded to allow build-up of unretained material in the recirculating water to a steady state, after which a further 7 sheets were formed, pressed and dried for testing. Target filler loadings were achieved within 2 percentage points in all cases. A cationic retention aid (Percol 292NS, BASF) was added to each furnish at a level of 0. 12% based on the total solids in the furnish. Paper properties were measured according to the relevant TAPPI standards. Filler contents were calculated from residual ash weights measured after placing sheets in a furnace at 450°C for 2 hours. At this temperature, no loss on ignition occurs for the calcium carbonate fillers used.

[00222] Example 2

[00223] Handsheets were made from a blend of bleached Kraft pulps, comprising 70% hardwood (Eucalyptus, UPM Uruguay) and 30% softwood (Pine, Metsa Botnia RMA90). These were co-refined in a laboratory Valley beater to a freeness of 450ml CSF (28.5 °S.R.). Each sheet was made to a target substance of 80gsm, with target filler contents of either 20% or 30% by weight. [00224] MFC was produced by co-grinding Botnia RMA90 bleached Kraft Pine pulp with a standard filler grade ground calcium carbonate (GCC, Intracarb 60, 60% < 2μm by weight, d50 1.4μm, Imerys), at a 50/50 ratio by weight, using a stirred media detritor mill.

[00225] Either GCC (Intracarb 60) or scalenohedral PCC (Syncarb S350, Omya, 3.5 μm d ₅₀ ), were added to the furnish for each sheet so that its total filler content, including the filler added with the co-ground MFC, would match the target value for the final sheets.

[00226] Paper properties of the formed handsheets are shown in Error! Reference source not found, below.

Table 2

[00227] Table 3 below and Fig. 1 show the relative change in key properties of each composition compared with the reference sheets filled with 20% GCC. Increase of filler content to 30% with GCC causes a significant loss of mechanical properties, which are partially restored by the addition of 3% MFC. Switching from GCC to the coarse PCC at 20% loading causes a significant increase in bulk and stiffness at the expense of tensile index and Scott Bond, and further increase to 30% PCC reduces the latter to below the level of the GCC, whilst also reducing stiffness to below the reference. The addition of 4% MFC restores the stiffness to within 5% of its original value, whilst providing improvements in bulk, Scott Bond and light scattering over the reference.

Table 3

[00228] Example 3 [00229] Handsheets were made from a blend of 95% bleached Eucalyptus Kraft pulp and 5% bleached chemi-thermomechanical pulp (BCTMP). The Kraft pulp was refined in a laboratory Valley beater to a freeness of 330ml CSF (37.5 °S.R.). Each sheet was made to a target substance of 75gsm, with target filler contents of either 25% or 35% by weight.

[00230] MFC was produced by co-grinding bleached Eucalyptus Kraft pulp with a standard filler grade ground calcium carbonate (GCC, Hydrocarb 60, 60% < 2μm by weight, d50 1.4μm, Omya), at a 50/50 ratio by weight, using a stirred media detritor mill.

[00231] The reference sheet contained 25% GCC. For all the other sheets, 2% MFC was added, and a blend of GCC (Hydrocarb 60) and scalenohedral PCC (3.1 μm d50, obtained from a satellite PCC plant at a paper mill) was added to the furnish for each sheet so that its total filler content, including the filler added with the co-ground MFC, would be 35%, and the proportion of PCC filler in the blend would be a fixed value between 0 and 100%.

[00232] Paper properties of the formed handsheets are shown in 4 below.

Table 4

[00233] The effect of changing from GCC to coarse PCC is shown in Error! Reference source not found, to Error! Reference source not found, below. Error! Reference source not found, shows that increase of GCC filler from 25% to 35% causes a substantial drop in bending stiffness, even with addition of 2% MFC, but substitution of the added GCC with the coarse PCC restores it to the reference value. Error! Reference source not found, shows that substitution of GCC with PCC increases the light scattering coefficient of the paper beyond that already achieved by the increase in filler content. Error! Reference source not found, and Error! Reference source not found, show that, despite the addition of 2% MFC, in this highly refined furnish there is a slight drop in tensile index and Scott Bond with the filler increase, but the substitution of GCC with PCC does not affect this substantially.

[00234] Example 4

[00235] Handsheets were made from a blend of bleached Kraft pulps, comprising 70% eucalyptus and 30% pine. These were co-refined in a laboratory Valley beater to a freeness of 350ml CSF (36 °S.R.). Each sheet was made to a target substance of 80gsm, with target filler contents ranging between 16% and 35% by weight.

[00236] Either a standard filler grade scalenohedral PCC (2.3μm d50, obtained from a satellite PCC plant at a paper mill) or a coarse grade scalenohedral PCC (Syncarb S300, Omya, 3.0 μm d50), were added to the furnish for each sheet so that its total filler content, including the filler added with the co-ground MFC, would match the target value for the final sheets.

[00237] Paper properties of the formed handsheets are shown in 5 below.

Table 5

[00238] Error! Reference source not found, shows that for a constant tensile index, the addition of 1% MFC allows an increase in filler content of 3.5% with the standard PCC, but 6% with the coarser PCC.

[00239] Error! Reference source not found, shows that light scattering increases by 100 cm ² g ^-1 for a 3.5% increase in the standard 2.3μm filler, and by 80 cm ² g ^-1 for a 6% increase in the coarse 3.0μm filler.

[00240] Error! Reference source not found, shows that these increases give equivalent stiffness for the 2.3 μm filler, but an increase of 0.04 mN m (7%) for the coarse 3.0μm filler, cc [00241] Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. The scope of the present invention is not intended to be limited to the above Description, but rather is as set forth in the following claims.

[00242] Use of ordinal terms such as "first," "second," "third," etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[00243] The articles "a" and "an" as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to include the plural referents. Claims or descriptions that include "or" between one or more members of a group are considered satisfied if one, more than one, or all of the group members are present in, employed in, or otherwise relevant to a given product or process unless indicated to the contrary or otherwise evident from the context. The invention includes embodiments in which exactly one member of the group is present in, employed in, or otherwise relevant to a given product or process. The invention also includes embodiments in which more than one, or the entire group members are present in, employed in, or otherwise relevant to a given product or process. Furthermore, it is to be understood that the invention encompasses all variations, combinations, and permutations in which one or more limitations, elements, clauses, descriptive terms, etc., from one or more of the listed claims is introduced into another claim dependent on the same base claim (or, as relevant, any other claim) unless otherwise indicated or unless it would be evident to one of ordinary skill in the art that a contradiction or inconsistency would arise. Where elements are presented as lists, (e.g., in Markush group or similar format) it is to be understood that each subgroup of the elements is also disclosed, and any element(s) can be removed from the group. It should be understood that, in general, where the invention, or aspects of the invention, is/are referred to as comprising particular elements, features, etc., certain embodiments of the invention or aspects of the invention consist, or consist essentially of, such elements, features, etc. For purposes of simplicity those embodiments have not in every case been specifically set forth in so many words herein. It should also be understood that any embodiment or aspect of the invention can be explicitly excluded from the claims, regardless of whether the specific exclusion is recited in the specification. The publications, websites and other reference materials referenced herein to describe the background of the invention and to provide additional detail regarding its practice are hereby incorporated by reference.